Nature's Pharmacopeia: A World of Medicinal Plants

Chapter 1


Concepts of Ethnomedicine


An herbalist portrayed in Quechua folk art, Peru. (Paint on wood [twenty-first century])

Around 60,000 years ago, groups of humans began to venture out of their southern African center of origin and colonize new areas. Consummate explorers, some marched through eastern Africa and onward to Europe, others into Asia and beyond.1 As they traveled, they encountered new plants and animals and perhaps new illnesses too. By nature curious, they undoubtedly tasted hundreds of leaves, roots, fruits, and seeds along the way. As they settled into lives in their new homelands, they developed a rich knowledge of which herbs were poisonous and at which times of the year. They learned which plants to gather for sustenance and eventually how to propagate them to support their growing communities. Existence was challenging for these early human explorers and colonizers. Fortunately, wherever they traveled, people discovered plants that fortified their bodies, healed their wounds, eased their pains, and affirmed their faith in the spirits that watched over them.

Communities maintained oral traditions, and in time some developed the ability to document their experiences with medicinal plants in art and writing. Archaeological evidence places the use of medicinal plants to as early as 5700 B.C.E. in Europe and approximately 4100 to 3500 B.C.E. in Asia.2 Records describing the medicinal properties of plants date to at least 2500 B.C.E., when ancient medical-religious texts of India describe herbs as components of the “knowledge of life.”3 Around the same time, the Yellow Emperor in China is chronicled in legend as having documented an array of curative plants.4 In Egypt around 1500 B.C.E., papyri record that garlic (Allium sativum) and juniper (Juniperus spp.) were used for their healing abilities.5 This evidence in written form shadows the tradition linking herbal knowledge across generations in the development of a medicospiritual discipline. In North and South America, Australia, and Africa, people practiced medicine and passed on their expertise, and by the time the Europeans encountered these peoples, elaborate health beliefs and vast herbal resources existed.6 Indeed, societies from Asia to Europe and the Americas likely independently developed their worldviews and ideas of wellness, philosophies in which plants were integral.

Before the systematic study of anatomy, notions of germs, and the advent of clinics, humans constructed detailed scenarios to explain the circumstances conducive to health and to remedy conditions of illness. In various forms of traditional medicine, people entrusted their physical, mental, and spiritual wellness to a framework of beliefs shared by members of the same community. Interestingly, some of these health-related ideas, while embraced by societies living far apart, share certain elements. For example, one such shared principle in traditional medicine is the belief that human health reflects a balance of forces or energies. When observing the world around them, early societies recognized that natural phenomena can frequently be described by terms in sets of opposites: light and dark, hot and cold, wet and dry, among others. A harmonious natural environment, these observers reasoned, was one in which neither heat nor cold is to an extreme, in which periods of dryness are followed by rain, and they expected a balance of such contrasting forces to promote life and vigor. The human body, being part of the natural world, also expresses such conditions. Thus when the body loses its balance, illness results, and balance can be restored through spiritual exercises, physical manipulation, and medicinal herbs. This equilibrium must occur in the individual as it does in the world and in the universe, in which the same forces occur and are usually at balance. The idea that health is a function of balance is among the most widespread of the traditional medical beliefs, evident in ancient China, India, the Mediterranean, and the Americas.7 It also demonstrates that in many societies, medicine was inseparable from philosophy and religion.

As people settled in many different regions of the planet, they harvested native plants for medicinal purposes and cultivated those they brought from elsewhere or acquired in trade. The combination of locally sourced flora, particular landscapes and physical challenges, distinctive languages, cosmologies, and social structures together imparted unique characteristics to the world’s many types of indigenous medicines. Rather than look at any region as uniform in terms of medical culture, it is worthwhile to consider the diversity in health-related beliefs and practices along several dimensions.

First, numerous ways of treating health can exist at the same time among a group of people—that is, medical plurality. For instance, different practitioners living in a single community may have vastly divergent approaches to addressing a patient’s condition, and individuals may address medical concerns with a combination of professional assistance and self-care. Second, health-related ideas evolve over time, adapting to new illnesses, accommodating changing philosophies, and incorporating innovations. Therefore, a regional medicine as practiced now or in the past, though it may be dubbed “traditional,” is not a static entity but rather dynamic. Third, cultural borrowing can lead to a synthesis between local medical knowledge and that appropriated from other people. While some forms of medicine have developed in isolated communities, many indigenous medical practices bear witness to years of commerce and exchange. Many of the world’s major traditional medicines are complex amalgamations of beliefs and techniques, employing pharmaceuticals having originated in different places.

The following sections provide an overview of some of the traditional medical beliefs and practices of East Asia, South Asia, Africa, and the Americas and demonstrate the diverse ways that people have conceptualized health and the role of plant-based treatments in influencing it. The remainder of the discussion follows the European experience in medicine, where, as elsewhere, health was considered to be the product of a balanced physical, mental, and spiritual state. In recent centuries, an approach to medicine emerged in Europe in which the scientific testing of herbs offered new ways to gauge therapeutic activity while rejecting many previous ideas about disease causation. Now widespread, particularly in the industrialized world, this biomedical system of health care coexists with numerous traditional medical systems and countless informal and folk practices that also employ plants as medicines.


Many of the world’s medical traditions developed concepts of health that viewed the person in the context of society, the local environment, and the universe as a whole. In these systems, the body is the beneficiary of natural energies (in the form of food and environment) and supernatural forces (such as spirit powers) that promote proper development. In China, people came to believe that the whole organism is healthy when it is in a state of balance and harmony with the world. In this system, health is considered a state of physical and mental well-being.8

Chinese traditional medicine9 views the universe as permeated by the qi life force, which constantly flows through heaven, earth, and all living things. Since qi is present in the air, soil, food, and all parts of the environment, it can strongly influence human health. The properties of qi are believed to change according to the time of day and the seasons, and they can vary regionally as well. For example, qi has a warmer quality in the summer and a cooler quality in the winter, darker properties at night and lighter properties during the day. According to Chinese medicine, illness results when an individual is unable to adapt to the changing nature of qi.

These ever-fluctuating features of the universe are the foundation of Chinese medical thought. Chinese medicine recognizes that qi and all matter are endowed with two opposing qualities: yin, the dark and cool property, and yang, the light and warm property. In the body, as in the environment, neither quality should have complete reign. For example, when night falls, the sky becomes quite dark. But in the darkness, there is light in the coming dawn. The cycles of day and night, the four seasons, and the patterns of precipitation and drought are natural processes of a universe at balance. As yin properties increase, yang properties decrease, until the extreme, when yang properties appear again. Because human beings are part of the universe through which qi flows, the yin and yang qualities of the body, changing over time relative to each other, can affect the nature of its qi. As qi is the force for life, so too is it responsible for health and illness.

Chinese medicine views that the body processes qi to derive nutrition and protect itself from illness. Properly extracted from the universe, a type of qi known as orthopathic qi gives the body the means to resist illness. Meanwhile, the illness-causing heteropathic qi assaults the body from the exterior, putting two types of qi in opposition. The ability of orthopathic qi to resist heteropathic qi is considered a state of health. Any overabundance of heteropathic qi activity can lead to illness, as can an excess of orthopathic qi: the healthy state is a balance of these forces. Since qi is influenced by its yin and yang properties, illness is thought to emerge from changes in the environment (disrupting a balance by affecting heteropathic qi) and/or changes in the body (affecting orthopathic qi).

To promote the proper qualities of orthopathic qi (and thereby resist illness), practitioners of Chinese medicine are aware that yin and yang qualities in balance promote health. (This does not mean a balance of equal amounts. In Chinese medicine, the yin–yang relationship in a patient is dynamic and responsive to the state of illness and the environment.) To maintain health, they pay close attention to the emotional state, social activities, diet, and exercise regimen, all of which influence the type and movement of qi in their bodies (figure 1.1).

Belief in the role of qi in health influences lifestyle by encouraging balance in all activities: maintaining an even emotional keel, striving for social harmony, consuming cuisine with an appropriate representation of “warming” and “cooling” ingredients, and undertaking regular physical and mental pursuits. When illness strikes, however, doctors can identify patterns of colors (of face or tongue), temperatures, pulse profiles, and behaviors that indicate to them whether the patient suffers from an overabundance or deficiency of yin or yang qualities.

Medical interventions are developed to strengthen the patient’s internal qi and improve its flow through the body by imparting to it the yin or yang properties that would allow it to promote health and drive out illness.10 Chinese pharmaceuticals, which are composed of plant material as well as some mineral and animal-based substances, are commonly given in mixtures of several ingredients, often prepared as soups or pills (figure 1.2). When choosing a treatment, doctors look to influence the balance of yin and yang activities. The Chinese herbal pharmacy is extensive, containing thousands of ingredients categorized by their warming or cooling properties and effects on the body’s qi.11 For example, the seed of milkvetch (Astragalus complanatus) is thought to support yang, and the stems and leaves of the dendrobium orchid (Dendrobium spp.) to strengthen yin.12 Chinese medicine also values herbs that serve to reinforce orthopathic qi in general, such as ginseng (Panax spp.) root.13 In summary, traditional East Asian medicine considers health to be a condition of balance, in which a person’s body and mind are at harmony with universal forces. Medicinal plants, selected according to their yin–yang properties, are thought to reinforce the body’s abilities to ward off illness.


FIGURE 1.1   A chart of a meridian through which qi flows, according to Chinese traditional medicine. (Wellcome Library, London, L0012239)


FIGURE 1.2   A pharmacist preparing a traditional Chinese herbal formula in Beijing, China. The wall behind the pharmacist is made up of hundreds of drawers containing dried plants.


Among the principal indigenous medicines of South Asia are ayurveda, a form of health care that originated in what is now northern India and Pakistan, and siddha, which is more widely practiced in the Tamil-speaking parts of southern India.14 In ayurvedic medicine, human beings are considered to represent a microcosm consisting of the same energies and substances as the larger universe, and therefore health is fundamentally connected to the state of the macrocosm.15 The basic matter of the cosmos combines to create the internal forces that govern physiology and behavior, the doshas. The doshas regulate various bodily functions and are seated in different parts of the head, chest, and abdomen. When they are in balance, a person is healthy.16 The state of equilibrium is influenced by, and can influence, the physical and mental constitution of the individual, so treatments frequently entail changes in religious or meditative behavior, emotional control, exercise, diet, and sensory experiences in the pursuit of balanced bioenergetic principles.17

Ayurvedic medicine recognizes that the flavors of food signal their elemental makeup and, therefore, their effect on the doshas. For example, sweet flavors increase one of the doshas while decreasing the other two, and pungent flavors raise two of the doshas while subduing the third. In total, ayurvedic medicine distinguishes six tastes that can be further classified by their hot-cold, oily-dry, heavy-light, and dull-sharp aspects.18 Therapeutic approaches in Indian medicine often entail changes in diet and the use of herbal pharmaceuticals with flavor and other properties conducive to the equilibrium of the doshas. For instance, the three spices of black pepper (Piper nigrum) fruits, long pepper (Piper longum) fruits, and the underground stems of ginger (Zingiber officinale) are widely employed in South Asia for their culinary, and therefore medical, properties. In addition to taste, color is considered important in its effects on the doshas. Because sensory experience plays a role in health and illness, ayurvedic pharmaceuticals draw heavily from fragrant and colorful plant products, including saffron (Crocus sativus) and turmeric (Curcuma longa).

Drawing on some common sources with ayurvedic medicine and other influences, siddha is a prominent form of health care in the state of Tamil Nadu in modern-day southern India.19 In this system of medicine, properties of the universe are at play in the human body in the form of matter (shiva) and energy (shakti), and they influence the health of the organs through their connections to the celestial zodiac.20In siddha medicine, health is a function of five elements that combine in various ways to form three bodily constituents, the muppini, whose equilibrium promotes health.21 In addition to environmental, climatic, and hereditary factors, the diet and a vast array of pharmaceuticals can play a role in the balance of muppini. Among many mineral and metal-based treatments, siddha medicine also employs herbal medicines to purify inorganic drugs before use, cleanse the body internally and externally, and treat specific ailments and generally improve health.22


In North America, the indigenous peoples developed approaches to health care that suited their diverse cultures and geographic settings. It would therefore be impossible to consider them as a bloc. However, a few examples will illustrate that among some American Indian groups, illness and healing has centered on the role of the community and the spiritual world in the well-being of the individual. In these traditions, physical and mental health is seen to be a result of a good relationship with one’s community, environment, and deities.23

Among the Iroquois (Haudenosaunee) of what is now the northeastern United States, for example, the health of the individual is inseparable from the state of the universe. Human illness is considered a response to harm that has occurred elsewhere in the social group or in nature.24 The Iroquois generally do not view health in the material (by attributing wellness to the forces, elements, and opposing qualities comprising the universe). Rather, they see health encompassing abstract criteria ranging from physical and mental comfort to the maintenance of life and good luck. Therefore, Native American herbalists integrated medicine into the community-wide sense of fortune, harmony, and spiritual oneness. Plant drugs are chosen to treat the spiritual imbalances in individuals or their surroundings, which reduces the physical manifestations of those conditions.

Because the source of health and illness has often been seen as existing beyond the material world, communities relied on specialists who claimed to mediate and communicate with the intangible, spiritual component of the universe to effect healing. It is often the role of shamans to care for the ill, harnessing their special powers to identify and appease the source of illness. It is also clear that many tribes view health as a community matter, and so healing takes place in ceremonial settings, such as sweat lodges and talking circles, under the supervision of an individual thought to have the power (or skill) to guide the process.25

Among the Chippewa (Ojibwe, Anishinaabe) of north-central North America, promotion of health and long life has been thought of as a matter of the spirits as well. Shamans adept at diagnosing and treating illness, sometimes called medicine men, are esteemed in their communities for their ability to identify the appropriate treatment for an ailment, knowledge that they believe they receive in dreams.26 In addition to remedies of physical ailments, Chippewa medicine men consider the preparation of good-luck charms as part of their healthcare duties. Therefore, they are known to provide patients with substances to attract mates or improve their hunting and fishing success (figure 1.3).27


FIGURE 1.3   Indigenous North American spiritual medicine. Among the Chippewa, shamans had special healing knowledge, including the use of medicinal plants: (top) a shaman preparing medicine; (bottom) a shaman treating a patient by drawing out illness. (Engravings from W. J. Hoffman, The Mide’wiwin or “Grand Medicine Society” of the Ojibwa [1891]; Project Gutenberg)

The notion that an individual’s mental, physical, moral, and spiritual health is interconnected with the well-being of the community is evident in the beliefs of the Lakota people of the North American Great Plains.28 The Lakota consider that a person comprises “four constituent dimensions of self,” including an individual soul or spirit, a divine spirit, a “vital breath” that sets the physical operations of the body in motion, and an intellectual-spiritual presence that guards against evil and helps overcome obstacles in life.29 In these traditions, medicinal plants serve to not only alter the physiology but also contribute to the fortune and social well-being of an individual or a community.

Thousands of plants serve these roles in indigenous North American medicine, and they are often used for different purposes in different regions.30 The big sagebrush (Artemisia tridentata) has been employed against respiratory illnesses such as the common cold, as a remedy for stomachache or headache, and as a spiritual cleanser.31 In what is now the western United States, people turned to native yuccas (Yucca spp.) for medicine, and, like many medicinal plants of North America, they are thought to influence physical and spiritual health. The Blackfoot, Cheyenne, and Lakota, for example, harvested the small soapweed (Yucca glauca) for use as a hair wash and baldness preventer, among other uses, and the Navajo (Diné) considered it a stimulant and contraceptive.32 The Hopi prepared extracts of the related narrowleaf yucca (Yucca angustissima) in ceremonial purification rituals in addition to using it as a hair loss–preventing shampoo and laxative.33

It is difficult to determine the extent to which indigenous American medical practices were codified because most groups left no written records. It seems the role of healer or shaman was often a matter of bloodline and special knowledge.34 Therefore, there are no ancient books describing practices as they occurred in the past and no way to determine the course of development of treatments, such as medicines shared between groups and how medicines may have diverged. Despite the enormous diversity of geographic settings and cultural histories, it is clear that indigenous Americans employed herbal medicines extensively for a variety of physical, mental, and spiritual conditions. Among many groups, plants served to promote health as a harmonious relationship between the person, his community, nature, and the spiritual universe.

The Aztec (Mexica) civilization, which flourished in present-day Mexico from the fourteenth to sixteenth centuries, left documents and descendents that shed light on its medical beliefs and practices.35According to indigenous mythology, the first humans were created from a divine mixture of material from the heavens and the earth, imbued with opposing properties that must remain in balance to sustain life. Disequilibria of these elements cause illness. The Aztecs viewed the earthly component as the Great Mother, instilled with feminine, cold, wet, and dark qualities. The Great Father was the heavenly contribution, a masculine, hot, dry, and light force.36 At its core, the Aztec worldview framed a parallel between the organization of the human body and that of the universe, where each bodily function owed something to either the Great Father or the Great Mother.

Aztecs sought balance in their diet, moderation in their emotions and physical activity, and obedience in their relationship with authority as a way to procure the harmonious relationship among the opposing forces that formed their bodies.37 The ultimate manifestation of harmony between a person, the community, the environment, and the cosmos was the tonalli, an energy-laden spirit from the gods that gave a person vigor.38 Various factors, such as immoderate physical activity, were thought to diminish the tonalli and result in illness.

The Aztecs also believed that humans, being made of cosmic material, could influence the fate of heaven and earth. Therefore, they developed means to “give back” to their creators in the form of human sacrifice, which they believed supplied energy to the gods.39 In addition to the belief that health derives from a balance of opposing properties in the body, the Aztecs held that spirits inhabited the forests, caves, rivers, and other features of the environment. These invisible beings, according to Aztec medicine, had a hunger for tonalli.40 Among the herbs that could protect the tonalli was tlacopatli (Aristolochia anguicida), “used to treat cold illnesses and to strengthen and revive people.”41 Children wore tlacopatli bead necklaces as a remedy, and its roots could be applied to the top of the head to restore tonalli.

Some illnesses were caused by, rather than cured by, plants, and the Aztecs harbored beliefs that affronts to plants or their spirits could invoke retribution. For example, people were forbidden to urinate on the aquiztli vine (Paullinia fuscescens), or else they would be afflicted with blisters all over their bodies.42 (The same plant was used to treat blisters.) Someone who slept in the shadow of aquiztli would lose his or her hair.43 Furthermore, some plants contained spirits that practitioners could take inside their bodies to derive otherworldly capabilities. For example, herbal drugs that induced visions were thought to function by transferring the god of the plant into the person ingesting it and by directing the user’s tonalli toward the god’s place of residence. Specialists sought such medicines to help them commune with deities and obtain secret knowledge to diagnose and treat patients in their care.44 Therefore, among the Aztecs, plants (and their spirits) played important roles in both causing and curing illness.


Those who employed plants to treat illness and promote health bore many titles in various historical and geographic settings. In this book, the terms “doctor,” “practitioner,” and “physician” refer to a health-care provider in a general sense. The reality of health care is far more complex than it is possible to explore sufficiently here. Over time and in different parts of the world, health advice and pharmaceuticals have been dispensed by religious leaders, village herb gardeners, midwives, and university-educated specialists. The roles of such diverse medical providers were determined by cultural standards that changed over the centuries. In ancient Greece, for example, those who called themselves doctors worked alongside (and competed with) exorcists, bonesetters, root gatherers, priests, and others.1 By the European Middle Ages and Renaissance, physicians exerted responsibility for a patient’s health based on a knowledge of medical theory, and surgeons and barber-surgeons performed manual operations such as cutting, excising, bloodletting, and tooth pulling, the last profession also trimming hair. Meanwhile, druggists, apothecaries, and alchemists provided medicinal substances with or without physicians’ prescriptions. At the same time, midwives and experienced female practitioners called wise women treated many patients, often with expertise in the areas of fertility and childbirth. Likewise, in Asia, Africa, and the New World, health practitioners include those with and without formal training, whether as doctors, drug preparers, shamans, tribal leaders, medicine men, priests, or scholars. Importantly, all these various specialists have knowledge of the use of plants to treat those under their care. Therefore, the study of medicinal plants can consider the ways that herbs are prepared and administered by people working at many levels and in numerous niches of a complex health-care environment.

1. Roy Porter, The Greatest Benefit to Mankind: A Medical History of Humanity (New York: Norton, 1997), 54.


The many forms of African medicine originated among peoples living throughout a vast continent, maintaining distinctive languages and social customs, practicing different religious traditions, and harvesting medicinal plants particular to their locations. To the West African Akan people of modern-day Ghana, illness results from a combination of social, environmental, and spiritual factors. Poor diet or overindulgence in certain foods can result in sickness, as can the forces of pathogen-laden wind, evil intentions, and the acts of evil people, spirits, and witchcraft.45 Healers prepare a variety of plants as herbal teas, salves, baths, and so forth, and some have special abilities to communicate with the spirit manifestations of the creator residing in the ocean, rivers, mountains, and plants.46 In addition, talismans play a role in helping practitioners select medicinal plants for their patients and improve the therapeutic outcome.47 For instance, the root of a forest tree that goes by a local name signifying “executioner medicine” (Mareya micrantha), apparently because of its poisonous effects if prepared incorrectly, is employed in spiritual baths and enemas, and its leaves are used to treat stomach pains and constipation, among other conditions.48

Among some southern African groups, such as the Basotho of modern-day Lesotho, health is a product of a body and mind at ease with the environment and spiritual world. Illness can occur when a person is in a state of physical or social disequilibrium, such as having an overabundance of certain substances in the body or having a disturbed social relationship with certain living or deceased people.49 The state of imbalance presents itself in a number of forms, such as having excess heat (in a figurative sense, rather than fever), which can be treated with cooling drugs “such as ash, water plants, or aquatic animals.”50Illness and misfortune can often be attributed to malevolent spirits and people with evil will, such as sorcerers, and therefore medical practitioners include herbalists, who are able to diagnose and treat many types of ailments, and diviners and seers, whose special powers to communicate with the spirit world render their diagnoses more accurate and their treatments (including herbal medicines) more effective.51 The special capacity of medicinal plants to influence a person’s luck is evident in the use of lemongrass (Cymbopogon marginatus) to procure love, as when a man adds it to his bathwater “while he calls out the name of the desired woman.”52 Other plants are less strongly associated with spiritual powers, such as lengana (the wormwood Artemisia afra), whose fragrant leaves are used as nasal plugs, in herbal teas, and for steaming in cases of colds, sore throat, and digestive problems, among others.53

To the ancient Egyptians, a body “in harmony with the cosmos … could serve as a receptacle for the vital forces that created the universe.”54 The Egyptians inhabited a universe composed of both physical matter and immaterial forces overseen by an assemblage of gods with varying responsibilities and powers. Accordingly, they sought to maintain health by regulating both physical aspects of their diet and behavior and by avoiding the ill will of deities who would harm them. Medical treatments commonly invoked the spirits to request relief from the various evils responsible for a person’s ailment. Therefore, to the ancient Egyptians, medicine, religion, and magic were deeply intertwined.55

Numerous herbal medicines and plant-derived dietary ingredients have been documented in medical papyri and survive as archaeological specimens.56 Among several hundred pharmaceuticals deciphered in ancient texts are many drugs that act in the bowels, such as the oil of castor seeds (Ricinus communis) and the fruits of the fig tree (Ficus spp.).57 To the Egyptians, regularly cleansing the evil toxins that accumulated in food prevented the spread of their harmful properties to the rest of the body. Therefore, castor counts among drugs recorded in the Ebers medical papyrus (ca. 1550 B.C.E.) to “drive out suffering from the belly of a man.”58


There are common elements in some of these diverse medical traditions. In many parts of the world, health conceptions tend to link an individual’s wellness to the state of the universe. The forces at play in the world also permeate the human body, contributing to vigor and longevity or, oppositely, illness. Good physical vitality and good fortune represent different aspects of health maintenance. Traditional philosophies stress the importance of balance in physical and mental activities, outlook on life, and choice of foods and spices. They often view psychological and physical health matters as deriving from common causes and sharing treatments. Plant-derived drugs tend to be classified within a scheme in which they serve to influence the vital force or restore equilibrium to the elements operating within a body, the effects of which reduce illness symptoms. In this sense, healers do not always seek to treat the ailment directly with their herbal preparations. Rather, they often treat the underlying imbalances causing the symptoms. In some cases, medicinal plants are used to communicate with and appease the deities or spirits responsible for illness.

The following sections will outline the evolution of the European lineage of medicine, from its origins in the ancient Mediterranean until the modern day.59 It is clear that traditional European medicine has much in common with other world medical systems, including the classification of life forces or properties into opposing but complementary categories, the idea that physical and mental health are tied together, and the use of herbal substances to promote harmony within the individual and more broadly. During the past several centuries, a new, scientific tradition emerged in Europe that embraced a distinctive methodology for determining effective medical treatments and that now serves as the foundation for practice in much of the world.


A group of Greek scholars including Hippocrates (ca. 450–370 B.C.E.) and his followers promoted the idea that the human being, as part of nature, “was subject to the same physical constraints as the rest of the ordered cosmos,” and therefore illness could be understood and addressed according to observable phenomena at play in the environment.60 Over many centuries, their theories were elaborated by doctors working throughout the Mediterranean region and served as the basis of an influential and widespread form of Greek and Roman medicine. To these thinkers, the universe revealed sets of opposing qualities—cold and hot, wet and dry, and so forth—and these principles joined in nature to create matter in the form of earth, air, fire, and water.61 The relative abundance of these temperature and moisture properties changed over time (such as in the cycling of the seasons), but early physicians believed that the four elements that they produced were fundamentally at balance.62 The human body generated from the elements a set of substances with properties corresponding to the principles of nature, which they called the humors. In this system, blood (or sanguis) is hot and moist, phlegm is cold and moist, black bile (or melancholer) is cold and dry, and yellow bile (or choler) is hot and dry.63 These substances were present in the body from conception until death, influenced by diet, seasons, and geography, and affected a person’s health and personality.

The four humors of traditional European medicine

•    Sanguis (blood)

•    Choler (yellow bile)

•    Phlegm

•    Melancholer (black bile)

The four humors of blood, phlegm, black bile, and yellow bile were metaphorical, invisible substances, not actually fluids that could be isolated.64 The blood humor is not the same as arterial blood, although when red blood emerges from a wound, the blood humor is instrumental. Similarly, phlegm is evident as a force behind watery secretions, black bile perhaps behind clotted blood and accretions in stool, and yellow bile in pus and vomit. People sought to achieve a relative balance among the humors, although individuals tended to be dominated by one of the four. Since the body generated humors from the elements present in the diet, and because the constitution drew influence from lifestyle choices, climate, and other factors, it was possible for imbalances to emerge that threatened the individual’s health. Conditions associated with an excess of phlegm, for example, include lack of appetite and thirst, weak brain, miscarriages, dysentery, diarrhea, and chronic fevers.65 Bronchitis and acute fevers would be rare among individuals with this excess.

The humors also played a role in shaping personality. The mental or psychological constitution of the individual—his or her temperament—could be classified according to the same principles. Someone with an excess of yellow bile was thought to be disposed to anger, particularly in the summer, and a person with too much phlegm might be passive and withdrawn, especially in the winter.66 Evidence for the classical belief in humors abounds in the modern English language and corresponds to the four temperaments of the ancient Greeks and Romans. Someone with a sanguine disposition is cheerful and optimistic. Phlegmatic means calm and composed. Melancholy is a gloomy or depressed state of mind, and a bilious individual is irritable and cranky.

Although some humoral imbalances were corrected surgically or by lifestyle changes, people often regulated the balance of humors with diet, a practice that includes medicinal herbs.67 The Greek writers who advanced the humoral system classified all foods and medicines by their fundamental qualities: hot, cold, dry, or moist. Remedies to illness were a matter of matching the personality and symptoms to a therapy with opposite properties.68 In this view, an excess of black bile, associated with the cold and dry temperament and indicative of conditions such as constipation and depression, could be relieved with the consumption of hot herbs such as senna (Senna alexandrina) and hellebore (Helleborus spp.).69 These medicines were thought to function by inducing the body to eliminate feces and, with it, the offending humor.

It is therefore not surprising that many traditional European herbal medicines derive from treatments intended to regulate the humors, with a particular focus on controlling the secretions of the body and the digestive process. Moreover, since excess humors were thought to accumulate poisons, a goal of pharmacy was to remove them from the body. So to purge toxins of the phlegm, yellow bile, or black bile, people sought herbal agents to induce vomiting and defecation. (Even in healthy times, medical wisdom held that frequent vomiting and purgation promoted wellness.)70 For example, scammony (Convolvulus scammonia) was recommended in early Greek texts as a purgative capable of effecting a rapid discharge of the bowels.71 Scammony remained in use for this purpose in Europe and the United States into the twentieth century.72

Medical writers during this period often framed therapies in terms of the humoral system, recognizing that drugs have temperature and moisture properties that could influence the temperament and symptoms of the patient. The Greek physician Pedanius Dioscorides (ca. 40–90) broke with tradition by presenting pharmaceutical knowledge in terms of specific effects on the human body, without interpreting medicine in the theoretical context of the humors (figure 1.4).73 His De materia medica (ca. 70 C.E.), a list of more than 500 herbs describing their names, appearance, and uses in the treatment of illness, was the first of its kind.74 Such a thorough catalog of medicinal plants was previously unknown in the Mediterranean sphere, and it served as a key medical text for the next 1500 years throughout Europe and Asia Minor. The value of Dioscorides’s work is in its descriptions of medicinal plants, which allowed others to gather the same herbs as he mentioned—an important step toward standardization in medical care—his instructions for preparing the medicines, and his inventory of the drugs’ uses and risks.

Because most medicinal substances were harvested from plants, and because Dioscorides produced the first book to treat drugs in this way, his influence was long lasting. A catalog of useful plant medicines became known as an herbal, and many important herbals have since been written. It is now commonplace to call all books listing medicinal plant properties materia medica in reference to the title of his work. Dioscorides’s materia medica also emerged as the first pharmacopeia—a list of all accepted drugs, with their preparation and processing for medical use—in the Western world.75 Since that time, national and international medical establishments have maintained written inventories of approved medicines. (“Approved” medicines are technically termed “official.”) In modern times, approval is often noted on the label of a medicine. For example, “USP” indicates a drug listed in the United States Pharmacopeia.


FIGURE 1.4   Pedanius Dioscorides, pioneer herbalist. (Woodcut after André Thévet, Dioscorides Arboriste [1584]; National Library of Medicine, B07205)


A list of medicines with their preparation and uses


The humoral understanding of health was first described by Greek physicians of the fifth and fourth centuries B.C.E. and elaborated in the writings of many others, including the celebrated physician Galen (129–ca. 216), living in the Roman Empire, on whose authority the practice of medicine in Europe depended for many centuries (figure 1.5).76 Galen’s theories on the nature of health satisfied the desire for a rational explanation of illness, and few doctors of his era or of succeeding generations questioned the elegance of the system in which balanced elements ensured health. In the medical tradition that he championed, the role of diet, lifestyle, and environment in health was paramount. In the centuries after Galen, the humoral system that had taken hold throughout Europe was codified into practice in Persia and then later throughout the Muslim world.77 Even when the glory of Greek and Roman scholarship waned, Muslim doctors preserved Galen’s medicine and reintroduced his writings to Europe hundreds of years later.78 With the revival of classical learning in Europe during the Middle Ages and Renaissance, humoral medicine again became the subject of intensive study, and Galen’s works were recopied and widely distributed. The humoral theories held sway in European medical education and practice until the eighteenth and nineteenth centuries, when they gradually began to subside. (It is worth noting that the Hippocratic-Galenic view of health was not the only form of medicine in existence in the classical Mediterranean region. Numerous schools competed for adherents during the era, a phenomenon that resulted in a large critical literature. In addition, many practitioners likely operated without an overarching theoretical framework or advocated religious or magical medicine. Ultimately, however, it was Galen’s writings that were elevated to the position of primacy for many centuries.)


FIGURE 1.5   Galen, promoter of the humoral system of medicine. (Lithograph by Pierre Roche Vigneron [ca. 1865]; National Library of Medicine, B012561)


With the fall of the Roman Empire in the late fifth century, medical practice in Europe became an amalgam of ancient Greek and Roman tradition, Catholic Church doctrine, and tribal folklore. The emphasis on natural forces and balance in lifestyle and dietary choices that Galen promoted became mixed with beliefs in the healing (or harmful) effects of spirit beings. For example, in the Leech Book of Bald, a tenth-century Anglo-Saxon herbal, treatments are described for illnesses caused by a “pagan charm” and “flying venom,” a clear departure from the idea that imbalances of body substances were at the core of illness.79

In addition to their generally herbal remedies, medical treatises of medieval Europe included prayers and incantations as disease preventatives or treatments. The practice of medicine was closely linked to the Catholic Church: doctors were frequently monks or at least associated with monasteries, the sites of infirmaries. In addition to healing salves, herbal amulets, and surgery, people turned to holy relics such as the bones of saints for their restorative properties.80

European medical practice in the Middle Ages was often imbued with mysticism and drew on local folklore. Herbs such as wood betony (Stachys officinalis) and peony (Paeonia officinalis) saw frequent use for ailments of the skin, bowels, and other complaints. In the medicine of the era, these plants were thought to work in part by warding off evil spirits and through astrological influences whose activities were responsible for illness. For example, an early medieval English herbal from the eleventh century recommends wood betony for eye pain, earache, and constipation, and to protect “a person from dreadful nightmares and from terrifying visions and dreams.”81 Peony root is said to be good for the pain of sciatica when tied onto the body and to cure “lunacy.”82 Some plants were thought to be particularly useful against spirit-borne illnesses and creepy-crawly threats, such as the greater periwinkle (Vinca major), whose description in the same eleventh-century herbal claims its utility “for possession by demons, for snakes, wild animals, poisons, for any threats, envy, terror, so you will have grace, so you will be happy and comfortable.”83

Many people also believed in the evil eye, a curse that penetrated their bodies and souls, bringing them misfortune and poor health.84 Fear of the evil eye probably goes back millennia, and it has persisted alongside other forms of medical belief.85 People produced charms from the leaves, stems, and flowers of medicinal plants to repel its malicious powers. Indeed, the same medieval English herbal suggests keeping mugwort (Artemisia vulgaris) in one’s house, as “it turns away the evil eye.”86

During the early medieval period, monasteries served as repositories of medical knowledge and centers of practice, where monks and nuns cultivated “physic gardens” of herbs and copied ancient Greek and Latin manuscripts.87 When medical colleges became established in Europe, they primarily taught the principles of Hippocrates, Galen, and other classical physicians in the context that prayer and divine will were the ultimate source of health.88 Complementing the church’s role in medicine was the oral tradition of folk medicine and home remedies passed down generation to generation and dispensed by spice and herb merchants (apothecaries) and elders.

By the sixteenth century, the European medical practice bore evidence of a complicated mixture of influences, including Galen’s humoral theory, Christian belief, and mystical folk traditions (figure 1.6).89Therefore, medicine encompassed beliefs in the fundamental forces of heat and moisture, whose balance allowed health, alongside divine providence, astrological forces, mystical energies, and curses. It was a complex discipline, and the bold Swiss alchemist-physician Paracelsus (Philippus Theophrastus Bombastus von Hohenheim, 1493–1541) sought to simplify it.


FIGURE 1.6   The four humors represented in a single person, with their astrological properties. (Woodcut by H. Steinmann [1574]; BIU Santé, 04059)

Paracelsus was a pioneering character in many ways (figure 1.7). He taught medicine in Switzerland, Germany, and Austria and broke with precedent by writing and lecturing in vernacular German rather than in Latin, as was customary.90 Considered one of the earliest toxicologists, he was the first physician to record that the dose of a drug can render it either poisonous or therapeutic.91 Most important, Paracelsus considered that the diversity of medical traditions, overrun by their various humors, spirits, incantations, and the like, obscured humans’ ability to perceive the natural healing abilities of plants. The theory of Galen and the superstitions of some religious sects, he thought, stood in the way of matching a medicinal herb to the ailment it treats. Therefore, Paracelsus promoted a simple, folk classification scheme for medicinal plants. Known as the Doctrine of Signatures, this belief held that the Creator designed plants with clues for the ailments they treated (figure 1.8).92 According to the Doctrine of Signatures, a plant growing yellow flowers is expected to cure jaundice, one with red sap would treat blood disorders, and one with fruit shaped like the brain, such as the walnut (Juglans regia), should be useful for improving mental abilities.


FIGURE 1.7   Paracelsus. (Woodcut by Tobias Stimmer [1587]; Wellcome Library, London, V0004456)

The long history of the Doctrine of Signatures in European medicine left a legacy in the common names of numerous plants that derive from their medical uses. For example, lungwort (Pulmonaria officinalis) grows leaves that bear a resemblance to diseased lungs with whitish spots and was used to treat lung infections such as bronchitis and tuberculosis.93 Liverworts (March-antiophyta) produce lobed leaf-like structures and were thought to be effective against disorders of the liver, which is also a lobed organ. The flowers of birthwort (Aristolochia clematitis) are reminiscent of a woman’s birth canal, and the plant was considered appropriate to treat obstetric concerns.94 Mandrake (Mandragora officinarum), a plant whose root can look vaguely like a virile man, was taken as an aphrodisiac and a fertility drug.95

The Doctrine of Signatures

A plant’s physical form offers clues about its medicinal uses.


FIGURE 1.8   The Doctrine of Signatures: (left) lungwort leaves, thought to resemble lungs; (right) plants with roots thought to resemble hands. ([right] Illustrations from Giovanni Battista della Porta, Phytognomica [1588]; Wellcome Library, London, L0030485)

During the sixteenth and seventeenth centuries, medical authority continued to coalesce around major medical universities, where scholars lectured and published in Latin, while a number of rogue physicians published herbals in vernacular. In the English language, some of the most influential herbals of this period were by John Gerard (1597), John Parkinson (1640), and Nicholas Culpeper (1652).96 The importance of plant medicines is underscored by the prominence of such herbals—catalogs of plants and their uses—as medical texts and field guides for apothecaries and herb gatherers. Because plants figured so prominently in human health, physician training included a thorough study of botany. It was also during this period that multiple new species were appearing in Europe for the first time, brought in from the east by traders and from the New World by conquistadors, missionaries, and natural-historian explorers. Many of these plants, too, had valuable medicinal properties. The description and classification of the diversity of plants on earth became a critical component of an advanced medical system.


Although the herbals documented hundreds of medicinal plants and provided doctors and plant collectors a guide to their use, it was not always straightforward for a person to identify the plants described because the field lacked a uniform naming system. The organization of species into clear groups with universally acceptable names, rather than local names that varied regionally, became the life’s work of the Swedish botanist-physician Carolus Linnaeus (Carl von Linné, 1707–1778). Among the general population, plants and animals bore local names that were not always geographically consistent, meaning two unrelated organisms could be described by the same name in different towns, and a single type of organism could go by many names. Before Linnaeus, a similar confusion could exist even within the trained botany community: physicians and herbalists sometimes used long Latin descriptions for plants that listed their attributes, but not in a universally standard format. As an example, take the description of the Persian buttercup in Gerard’s Herball, or Generall Historie of Plants: Ranunculus Asiaticus grumosa radice flore flavo vario (Asian crow-foot with lumpy root and yellow striped flowers).97 Gerard’s seven-word identifier might just delineate a color variety that he happened to encounter but not one that applies to all individuals of the same biological type. In any case, the long label is cumbersome. Linnaeus developed a hierarchical system that organized all the specimens he studied by similarities and differences in structure and resulted in each unique type being assigned a single, simple Latin descriptor.

This advance, first published in Systema Naturae (1735) and elaborated in the monumental two-volume Species Plantarum (1753), gave all unique plant types two names: a genus name, a broad category encompassing many physically related varieties, and a species name, a precise name delineating just one type of organism.98 This name, composed of a genus and species, is known as the Linnaean binomial, and it is the standard format by which scientists identify and distinguish organisms and varieties with precision.

Binomial nomenclature

The scientific naming system that universally describes a single type of organism using two names, genus and species

The logic of Linnaeus

The genus name is a noun, and the species name is an adjective describing it. For example, the white oak is Quercus alba (oak white), black pepper is Piper nigrum (pepper black), and the opium poppy is Papaver somniferum (poppy sleep inducing).

Over the centuries, new knowledge has been applied to Linnaeus’s classification scheme, and systematists (specialists in biological classification) refined the original hierarchies and species assignments. In particular, recent advances in molecular biology have allowed biologists to study the DNA of plants and ascertain evolutionary relationships not apparent to previous generations of researchers examining only the outward appearance of specimens. In some cases, molecular data have helped rewrite the classification of species by placing them among their closest genetic kin, despite differences in morphology.99

The binomial system pioneered by Linnaeus remains the only accepted way to identify an organism in the scholarly world. For example, the tomato plant can be properly described by its binomial Solanum lycopersicum (note the capitalized genus-name initial, lowercase species-name initial, and italics), which can be shortened to S. lycopersicum on subsequent references.100 There are other members of the genus Solanum, relatives of the tomato such as S. tuberosum, the potato. Occasionally, distinctions within a species become apparent (sometimes called subspecies), necessitating a special notation, and the binomial is appended. For instance, Origanum vulgare refers to oregano, the aromatic perennial herb native to Europe and western Central Asia. Origanum vulgare ssp. gracile is a particular type of oregano from Central Asia with a distinctive leaf shape and flower color, and Origanum vulgare ssp. hirtum has been selected for its ease of cultivation and strong flavor.101


By closely examining plant specimens and systematically describing their similarities and differences, Linnaeus demonstrated that careful observation, coupled with a willingness to break with long-standing intellectual customs, could lead to a new understanding of nature. Whereas much of European medicine sought to treat illness according to the prevailing conceptions of the humors and employed plant drugs chosen by convention or “signature,” the European Enlightenment period saw the growth of a movement to question and test medical ideas actively. This movement helped progress medical study from a discipline guided by theological and classical doctrine to one in which physicians refined old medicines and developed new ones by testing drugs and making careful observations of dosage, preparation, and patients’ outcomes. To some doctors of this era, no longer were mysterious spirits and invisible substances the primary agents in human health. Rather, they began to see human disease as a manifestation of symptoms with reducible physical causes, and they realized that the constituents of plant medicines could serve as remedies.


The notion that knowledge derives from systematic observation and experimentation

During this era, some physicians challenged the spirit-, humor-, and life force–based conceptions of illness and came to regard human health as an essentially mechanical phenomenon that could be influenced by quantifiable medications and interventions, such as specific doses of experimentally tested medicines. An important example of this developing style of medicine is the work of William Withering (1741–1799), an English physician and botanist who pioneered a treatment for the age-old malady known as dropsy (figure 1.9).102 The symptoms of dropsy include the accumulation of fluids in the extremities and lungs, shortness of breath, and a weak pulse. In today’s terminology, these conditions indicate congestive heart failure. Prior to Withering, treatment of dropsy frequently entailed piercing the patient’s extremities to release the excess fluid.103 Withering suspected that dropsy could be treated differently and sought to establish a new medical intervention.


FIGURE 1.9   William Withering. (Engraving by Henry Adlard [nineteenth century]; National Library of Medicine, 216167)

To develop a new treatment for this circulatory ailment, Withering turned to the experience of traditional herbal healers in England, who had been producing various plant concoctions for dropsy following folk practices dating back many centuries. He learned that among these treatments was the foxglove (Digitalis purpurea [figure 1.10]). “A lady from the western part of Yorkshire assures me, that the people in her country often cure themselves of dropsical complaints by drinking Foxglove tea,” Withering wrote, and he set about to examine closely the plant’s effects in patients.104 For ten years (1775–1785), he performed extensive studies to establish the best season in which to harvest the medicine, the most effective part of the plant, the proper preparation of the material, and the effective dose in carefully measured quantities of powdered leaf extracts. As foxglove was known to be poisonous, he needed to establish the drug’s therapeutic dose. At the correct dose, the plant’s cardiac glycosides work to slow and strengthen the heartbeat, reduce fibrillation, and improve circulation to clear retained fluids. (Through the twentieth century, the foxglove-derived medicine digitalis remained an important treatment for congestive heart disease.)105 Thus Withering’s exacting measurements and reliance on physical, rather than spiritual, evidence for the source and treatment of disease set the stage for a new approach to medicine that took shape after the eighteenth century.


FIGURE 1.10   Foxglove flowers.

In a break with earlier beliefs, some in the medical community of the nineteenth century began to accept that physical entities, such as germs or chemical toxins, were the cause of disease, rather than harder-to-measure forces such as curses or excesses of yellow bile. The body was viewed in mechanical terms, and advances in anatomy and the understanding of cellular structures encouraged physicians to concentrate their attention on the minutely observable processes of movement, development, and biochemical transformation in human beings. Whereas previous generations of doctors prescribed treatments based on the recommendation of ancient Greek scholars, with diagnoses and dosage never formally tested, some in this era saw prudence in examining the patient for specific symptoms and the drugs for unique active components. Many began to recognize the difference between traditional conjecture and empirical evidence for the efficacy of natural drugs.

While successful herbal medicines have developed—and remain in practice—throughout the world drawing on ancient philosophies and traditional expertise, a great number of herbs and herb mixtures have not yet been tested in a systematic way.106 Support for medicinal properties based on measured observation is central to the medical system that grew out of the European Enlightenment. In following practices elaborated during the nineteenth and twentieth centuries, biomedical researchers seek to test the effects on patients of carefully prepared and administered drugs across a broad spectrum of doses (including no drug at all), with data scrupulously recorded and shared with the wider medical community.


Based on the utility of empirical observation in gathering evidence about natural phenomena, biomedical research has evolved in recent centuries to develop a rigorous methodological platform from which to pose questions about the effectiveness of medicines and to generate answers to advance the discipline. This framework is known as the scientific method, and it serves to establish and support claims of a medicine’s value in treating disease. The scientific method consists of a multistep process.

Phases of the scientific method

1.  Hypothesis formation

2.  Experimentation and analysis

3.  Critical review, publication, and retesting

•    The first phase of this method is to develop, based on a great deal of prior research, a testable idea (known as a hypothesis) that can be addressed experimentally. For example, the notion that some chemical in foxglove is capable of reducing the symptoms of dropsy could be examined by giving dropsy patients known doses of the foxglove extracts and carefully observing the outcomes. Crucial to this step is the expectation that all measurements would be repeatable by others. That is, no “secret” plant extracts can be promoted, and all characterizations must be precise. Furthermore, all experimental outcomes must be based on natural observations and derive from physical explanations. In this sense, it is not appropriate to assign any biological activities to ghosts, spirits, life forces, hexes, or acts of God, because they cannot be measured or described with existing instruments.

•    The second phase of the scientific method is the process of carefully designing and carrying out a controlled experiment. To do this, the researcher must be able to distinguish whether a drug is truly responsible for (that is, causes) a perceived effect. For example, consider another experiment to test the efficacy of purple coneflower (Echinacea spp.) extract, an herbal treatment available in many retail drugstores, on the severity of respiratory infections. In this fictional experiment, fifty children suffering common cold symptoms are given daily doses of purple coneflower extracts, perhaps in the form of capsules. On the second day, half the patients report feeling much better, and by the fourth day, nearly all the children feel fine, an assessment supported by objective measurements of their body temperatures and open nasal passages. It might appear that the herbal remedy is effective—after all, most of the children recover, and quickly, it seems. The patients may even report that this herbal treatment seems more potent than alternative treatments taken during previous illnesses. However, biomedical researchers might challenge the evidence for efficacy because of the lack of experimental controls. Without experimental controls, it is not possible to determine whether the patients would have recovered, perhaps just as quickly, even without taking purple coneflower pills.

How can the researcher determine what the normal progression of the illness would be in the absence of any treatment? To establish this, each experiment can have a negative control treatment, in which a subset of the patients is given a false or mock medication intended to produce in itself no specific effect on the condition being studied. This treatment might consist of a preparation of medically inactive herbs or a sugar pill. The patients, however, are not informed which type of medication (“real” versus “mock”) they receive. The treatment not containing active medicine is called the placebo. In this way, the investigator can assess whether the pharmaceutical under consideration has any therapeutic effect distinguishable from the placebo. Since some drugs produce a range of physiological effects in addition to the targeted condition (called side effects), clinical researchers can employ placebos that cause mild side effects, a way to disguise further the nature of the treatment to the patient. These are known as active placebos.

Use of a placebo group in a clinical study is a key element of modern biomedical research that allows researchers to document the physiological and psychological aspects of treatment in a single experiment. Interestingly, many patients respond symptomatically to the experience of being treated in a medical setting, regardless of taking an active medication. In studies of pain, depression, and numerous other ailments, on average 35 percent of patients experience an improvement in symptoms after taking an inert medicine.107 This phenomenon, often called the placebo effect, can be traced not to the substance of the medication, which is thought to be biologically inactive, but to the treatment environment and the nature of the interaction between a patient and a caregiver.108 That is, the patient feels listened to and that his condition is understood, the patient feels concern from others, and the patient feels a sense of control over his own condition. Thus the mental outlook and optimism of a patient can strongly affect the physical sense of health.

Because the placebo effect is such a powerful factor in the manifestations of illness, experiments should account for it. The best clinical studies test a medication of unknown efficacy against a placebo among patients randomly assigned into the two categories. Neither the patients nor the caregivers know whether they are receiving or delivering the medication or the placebo, a design labeled “double-blind.” Since the advent of scientific medical practice, countless double-blind, placebo-controlled studies have contributed to a contemporary pharmacopeia of natural and synthetic medications.


The systematic, empirical approach to the study of nature employed during the eighteenth century in Europe contributed new methods toward determining the effectiveness of drugs. Researchers began to test carefully dosed medications given in similar ways to large numbers of patients, diligently recording the signs of disease before, during, and after treatment. Such observational activities were new to medicine and supplanted an earlier methodology of treating each patient individually following classical recipes and recording subjective outcomes, if any. A classic example of empirical medical research is the work of the English physician William Withering, who tested the effectiveness of precisely measured doses of foxglove extract on indications of the circulatory disorder dropsy by administering the drug to patients and recording their physiological responses. In this genre of observational study, a patient is given a drug, and then the outcome is monitored. Although the observational approach has noted merits, biomedical science recognizes flaws in its methodology.

Certainly, researchers want to know whether a drug has a physiological activity in the body. However, an observational study does not lead to clear cause–effect relationships. Is it the drug that causes the patients’ symptoms to change or not? In such experiments, for instance, the patients receive a dose of what they believe to be medicine from a doctor and, in many cases, feel better at the end of the trial. This improvement in the patients’ condition (objective and subjective criteria) is a perceived therapeutic effect. But can it be said that the patients got better as a result of taking the drug?

The perceived therapeutic effect, measured physiologically or as a subjective sense of wellness, may result from the drug treatment (that is, the components of the medicine itself) or from other factors that accompany such an observational study:1

Natural course of the disease. Many diseases, especially chronic ones, progress in periods of increased severity followed by remission (for example, cancers, arthritis, and depression), during which time the symptoms subside, even in the absence of medical treatment. A patient experiencing remission of a disease after taking medicine might erroneously attribute the lessening of symptoms to the curative power of the drug, even if the drug had no effect at all.

Concomitant treatments. Patients in observational studies sometimes engage in activities that may increase or decrease the severity of their symptoms in a way unrelated to the therapeutic effect of the drug administered. For example, they may change their exercise routine, alter their diet, or self-administer additional medications. In this situation, it is not possible to assert whether the particular medicine under study or the patient’s other behaviors are responsible for any change in the disease.

Therapist–patient interactions. To many patients, the experience of being cared for in a clinical setting is itself therapeutic. The trusting relationship between medical practitioner and patient might account for an improvement in disease symptoms by improving the patient’s mental state and sense of well-being. Therefore, the relationship between patient and provider might give rise to a general therapeutic effect in the absence of a specific (medicinal) therapeutic effect.

Hawthorne effect. This social-science phenomenon demonstrates that individuals who know they are under observation change their behavior. In short-term observational studies, patients assiduously follow their hygiene regimens and might perceive their health differently for no other reason than the awareness they are the focus of study.

Social desirability. Patients may seek to please their doctors by reporting their symptoms are less severe than actually experienced.

Biomedical research employs a particular methodology to test the efficacy of medicines in a way that accounts for potentially confounding factors of observational studies. By engaging in placebo-controlled, randomized, double-blind clinical trials, researchers seek to identify medicines with specific therapeutic effects and characterize their side effects in a robust manner.

Placebo-controlled. To ascertain whether a medicine under investigation produces a specific therapeutic effect, it is important to determine the effects of all other aspects of the test in the absence of the potential drug. This is known as a control, and it requires that all patients experience the same conditions of treatment except for the single element of the drug. Some individuals in such a test receive the drug, while some individuals receive a treatment that resembles the drug in all possible ways but that is thought to be physiologically inert. In clinical trials, for example, one group of patients takes a pill every week that consists of the herbal extract under examination, and the other group of patients takes an identically marked pill every week that contains simply starch. The mere administration of an inert medicine can have a therapeutic effect (known as placebo when a positive effect), and so this effect is accounted for as a placebo control. Among patients in a drug trial, any symptomatic improvement beyond the effect of placebo alone might be attributable to the effect of the medication.

Randomization. From a large population of patients, individuals are randomly assigned either to receive the medical treatment or to receive the placebo treatment. (In most cases, patients are advised that they have equal likelihood of participating in either test group but are never told to which group they belong.) The process of randomization avoids any selection bias in the medical treatment versus placebo treatment groups.

Double-blinding. Neither the patients nor the clinical staff are informed which individuals receive the medicine or placebo. In this way, none of the clinicians, through conscious or unconscious actions, behaviors, sympathies, or preferences, can influence the perceived therapeutic effect in either the medical treatment or placebo group disproportionately.

By clearly articulating an answerable clinical question, defining measurable, reproducible criteria for efficacy, and critically assessing the evidence, the clinical trial seeks to establish reliable causative links between a treatment regime and therapeutic usefulness. Such trials inform biomedical practice and establish the criteria by which pharmaceuticals in the United States and elsewhere are regulated. Much current research into determining the safety and efficacy of herbal remedies also employs these methods. Studies falling short of the standards of placebo control, randomization, and double-blinding call their findings into question.

Even the most carefully constructed trials face the challenge of critical assault, which is a desirable and positive aspect of the scientific process: researchers do not view their methods as perfect and constantly seek to improve them. Often many trials, enrolling a large number of patients and testing a drug across a wide range of doses, are necessary before scientific consensus can be reached on a drug’s possible therapeutic effects and risks.

1. These categories are based on those of Edzard Ernst, “The Importance of Having a Robust Evidence Base—A Personal View,” in Homeopathic Practice, ed. Steven B. Kayne (London: Pharmaceutical Press, 2008), 33–42.

•    The third phase of the scientific method is the publication and sharing of experimental findings with the broader community. To facilitate this, numerous scholarly journals specialize in printing such medical studies, and their editors and reviewers vet the studies for adherence to scientific guidelines and clarity of conclusions drawn. Published experimental results are then subject to criticism and retesting, a process that strengthens accurate findings and disproves false findings or improperly conducted experiments. Consequently, medical science constantly renews and improves its understanding of human health.

The scientific method, consisting of a carefully composed hypothesis to test, a controlled experimental approach, and the publication of findings, marks an important methodological shift from the practice of traditional medicine in Europe and elsewhere. In recent decades, medical authorities in Europe, the United States, and other parts of the world have emphasized the role of this system, with its clinical trials and statistically determined outcomes, in improving health care in both industrialized and developing nations. Although originating from the European Enlightenment, the scientific medical discipline has spread to many countries, where doctors are trained in its techniques and drugs are studied in certain standardized ways. It is this form of health care, coupled with progress in biochemistry and the strength of recent surgical advances, that is practiced as biomedicine around the world.109

Criteria for high-quality clinical trials

•    Placebo controls

•    Randomization of patients

•    Double-blinding


The biomedical approach has joined numerous other traditions in offering its own understanding of health and therapy in a diverse and dynamic health-care ecology. In the modern-day United States, for example, patients can seek treatment in hospitals and doctors’ offices, where they might be likely to receive pharmaceutical drugs prepared from natural or synthetic sources. Yet the same people may also visit a traditional herbal healer and purchase mixtures of plant products for their health concerns, grow their own herbs to make herbal teas, and follow their grandmothers’ dietary advice. In today’s China, medical universities train physicians to practice either biomedicine or Chinese traditional medicine, and patients can choose to seek treatment at clinics and hospitals specializing in either.110 In addition, those same patients might prepare cuisine at home according to traditional and religious principles, whether in terms of the heating and cooling properties of their foods or for their spiritual effects. They may also take medicines deriving from regional folk traditions. As in the past, many ideas about health and, consequently, many forms of herbal medicine coexist in the world’s communities.

Medical beliefs and practices evolve, rendering any glimpse of a tradition as written in a text or observed among indigenous people merely a snapshot in time. Among the ancient Greeks, ideas about the humors were vigorously debated. Originally, the Hippocratic system accounted for only three fundamental substances, with black bile added later.111 As these ideas were elaborated during Galen’s time and afterward, differences in interpretation and application of shared concepts abounded. In the Muslim world, Galen’s authority was reformulated by a series of influential writers over the course of several centuries, and forms of his teachings took hold in South Asia, Central Asia, and the Middle East, adapting to locally endemic illnesses and incorporating regionally abundant plants in therapy. In medieval and Renaissance Europe, Galen’s notions of the humors variously took on astrological and religious inflections. As the voyages of discovery brought back never-before-seen plant specimens to the learned physician-botanists of Europe, these scholars accommodated the novel herbs in the preexisting scheme and assigned to them the qualities of hot, cold, dry, and moist that would enable them to be used alongside a growing number of plants both inherited from the ancients and adopted from folk practitioners. Likewise, biomedicine has gradually developed its robust methodology over the course of more than a century, discovering new treatments and discarding older ones, a process that will continue.

Herbs in the context of medical treatment

An herbal medical treatment may yield outcomes, both positive and negative, resulting from the activity of the drug itself and from the setting of the treatment, the relationship between patient and caregiver, and the patient’s expectations about the experience.

Evidence-based medicine demands a rigorous, experimental demonstration of drug activity but cannot account well for other treatment effects.


A remarkable diversity of medicinal plant uses is evident in the written record of past cultures and among living practitioners who understand health according to their sometimes shared, sometimes divergent conceptions of the human being in nature. One goal of current scholarship is to learn about these people and their medicines in their own time and place. Another area of research seeks to apply the methodological standards of biomedical science to traditional medicines, to examine them for efficacy and risk. These approaches engage in experimental trials to obtain data that can be analyzed statistically, collect detailed case studies of patients in the clinic, and pursue biochemical assays in their quest for evidence of a treatment’s value in medicine.1

To biomedical researchers, the statements “this tribe has used plant X to treat headaches for centuries” and “these healers prescribe mixture Y all the time, and there haven’t been any problems with it” do not serve as medical evidence for the effectiveness of herbal remedies. They are anecdotes that document cultural practices but not data in support of the efficacy of any drug or treatment. The fact that a group of people exploits a plant or plant extract for a specific purpose does not demonstrate that it is effective for the intended or any other use. Nor does biomedical science view the medicine to be ineffective. Evidence-based medicine requires an experimental demonstration to support use of a novel drug. This foundation of methodological rigor has become institutionalized in the United States and elsewhere, for example, intrinsic to physician training and government regulatory decisions.

In recent decades, numerous plants drawn from traditional medical practices have been subjected to biochemical study and clinical trials to generate the sort of evidence expected by the biomedical establishment. Such experiments largely ignore some aspects of health so valued in many of the world’s medical traditions, such as the relationship of a person to the spirit world, the role of a person in the community, and the customization of a treatment to suit an individual patient’s condition.2 Indeed, the scientific method requires researchers to set aside the supernatural, to standardize experimental treatments, and to consider data mostly in terms of statistical averages rather than individual outcomes. The tenets of experimental science notwithstanding, many biomedical practitioners have come to embrace some of the social, spiritual, and holistic aspects of therapy common in traditional health care.

The world’s numerous medical traditions can treat those who believe in them, sometimes in ways that biomedical science has not yet fully addressed. On the one hand, some herbal drugs may have physiological activities thus far not demonstrated by clinical experiments. On the other hand, some medicine may work not because of the substance of the drug but through the social setting and expectations of those involved. In particular, academic investigators have only recently begun to study the role of the therapeutic relationship between patient and caregiver, one that can treat discomfort in the absence of drugs: “What is important is that doctors—healers of any sort or type—are convinced that their techniques are powerful and effective, and that there is undeniable evidence of this effectiveness. In some places, such proof comes from gods or spirits, in some places from personal experience, and in other places from the assertions of science.”3

1. A defense of the scientific method and critique of complementary and alternative medicine is in R. Barker Bausell, Snake Oil Science: The Truth About Complementary and Alternative Medicine (New York: Oxford University Press, 2007).

2. A critique of evidence-based medicine is in Steve Hickey and Hilary Roberts, Tarnished Gold: The Sickness of Evidence-Based Medicine (CreateSpace, 2011).

3. Daniel E. Moerman, Native American Ethnobotany (Portland, Ore.: Timber Press, 1998), 43.

Humanity’s many medical traditions have borne witness to significant cultural exchanges that produced new syntheses in various places and times (figure 1.11). For instance, South Asian siddha medicine is thought to be a fusion of an ancient southeastern Indian folk tradition with theories borrowed from ayurveda. Both ayurveda and siddha probably gained certain diagnostic tools, such as pulse diagnosis and uroscopy, from Greek medicine brought by Muslims.112 In modern-day China, biomedical concepts of disease have been interpreted according to traditional medical tenets, such that a patient in a traditional medical clinic might be diagnosed in terms of both yin–yang imbalance and abnormal hormone levels and be offered an herbal prescription as treatment. After many years of setting aside the spiritual and psychological aspects of therapy, some biomedical practitioners are promoting the approach of “treating the whole person” and “mind–body medicine,” the tenets of which clearly resonate with many traditional medical practices.


FIGURE 1.11   A Peruvian herbalist. This clinic treats illnesses such as cancer and anemia as well as the effects of witchcraft and evil wind, drawing on several indigenous herbal traditions.

The medicinal plants of the world are employed in a tremendous variety of human settings. Some are harvested for use in extensive health-care systems grounded in elaborate theory, with specialized hospitals and pharmacies and a worldwide audience, such as those used in biomedicine and Chinese traditional medicine. Plants such as coffee (Coffea spp.) are turned into commodities, sold in markets large and small, and take on importance in locally accented concepts of health and sociability. Still other herbs are used by small communities, by people whose unique understanding of nature may never have been recorded, and whose medical traditions may reside only in the expertise of a dwindling number of practitioners. All these facets of the human experience with medicinal plants, whether found in cosmopolitan parts of the earth or in isolated villages, whether drawn from a large scholarly lineage or a folk custom practiced by few, demonstrate the capacity of medicinal plants to shape our culture.

In many parts of the world, people developed medical traditions that incorporated plants to promote health and treat illness. Among them are schemes where opposing forces or substances find balance in the human body and where plants can help restore disequilibria that develop. Other conceptions involve the intervention of spirit beings in the individual’s health. Herbal remedies are employed in diverse therapeutic settings, some of which can be gleaned from ancient texts and others from the numerous peoples who have inherited a medicinal plant legacy. While medicine in Europe experienced many changes across the millennia, it had much in common with other world medical traditions until some of its practitioners developed an empirical and scientific approach during the eighteenth through twentieth centuries. As a result, biomedical researchers test drugs following a prescribed set of expectations in a controlled experiment. In this way, biomedicine has delineated a methodology that approaches disease as the product of physical dysfunction that can be remedied with specific pharmaceutical substances. In a world where numerous traditional medical practices coexist, the diversity of health-related beliefs and the mixture of practices provide a fascinating backdrop for medicinal plants in the modern day.