Modern research has shed much light on the chemical composition of herbs and how they work. For certain very powerful herbs, scientists have been able to identify a single constituent that stands out as the herb’s primary “active ingredient.” The anthraquinone compounds in purging buckthorn (Rhamnus cathartica), for instance, clearly are responsible for the herb’s strong laxative effect. Scientists have also identified many of the compounds that give culinary and aromatic herbs their familiar flavors and scents. For other herbs, especially those used medicinally, explanations are less clearcut. Scientists try to isolate active ingredients to better understand how herbs work, and some herbal products are “standardized” to a specific chemical—with the implication that the chemical is the single active component. But clinically oriented herbalists and others who study herbal therapies believe that the medicinal properties of most herbs derive from the whole plant—a synergy created by its constituents working together to produce a desired effect in our bodies. In this chapter, we explore phytochemistry—the study of chemical compounds made by plants—as it relates to our use of herbs for the treatment of health conditions and for the promotion of wellness.
PLANT CHEMISTRY: AN INTRODUCTION
Plant chemistry, also known as phytochemistry, is the study of the chemical compounds in plants. All living things on earth are made of chemicals. In fact, the chemical composition of plants and people is very similar. Both consist of common elements, including carbon, hydrogen, oxygen, and nitrogen. Chlorophyll—the green pigment essential to photosynthesis, the process plants use to transform water and sunlight into food—has been called “green blood” because its chemical makeup is similar to the hemoglobin in human blood. A molecule of chlorophyll and a molecule of hemoglobin each consist of carbon, nitrogen, and oxygen atoms, but in different proportions. There are other important chemical differences between hemoglobin and chlorophyll, but the basic similarities are striking.
Plants produce a variety of chemical compounds, called metabolites, as part of their normal life processes. Some of these compounds allow plants to store energy in the form of sugar, for example, while others, such as toxic compounds, help plants defend against diseases or predators. After all, plants cannot run away from insects and other animals trying to eat them! Some compounds might offer the plant a sort of evolutionary “fitness,” allowing it to survive and even thrive under conditions such as drought or an increase in average temperature that could wipe out other plant species.
There are two types of plant metabolites: primary and secondary. Primary plant metabolites include carbohydrates, lipids, proteins, and nucleic acids. These are compounds essential not only to the life of the plant but also to human health and nutrition. Plants use pieces of primary metabolites as building blocks to produce secondary metabolites. Secondary metabolites include terpenes, phenols, alkaloids, and their glycoside derivatives. These are largely responsible for the characteristic aromas, flavors, colors, nutritional values, and medicinal actions of the herbs and spices we use as foods, medicines, dyes, perfumes, and other products, from disinfectants to poisons. These properties also serve a vital purpose for plant life. For example, secondary metabolites give a flower its fragrance and color, both of which attract the pollinators the plant needs in order to set seed and produce the next generation of the species. The dividing line between primary and secondary metabolites is not always clear, and the two are integrally linked. Learning basic information about both primary and secondary metabolites will help you understand how they impact the properties and effects of herbs.
Primary Metabolites: Carbohydrates
Carbohydrates are essential to life and are part of the makeup of all living creatures. They provide animals, including humans, with energy and fiber and are the basic building blocks for all other plant chemicals.
Carbohydrates are composed primarily of sugars (saccharides) whose molecules are arranged in particular ways. Monosaccharides, for example, contain 1 sugar unit (mono means “one”), while polysaccharides contain 10 or more sugar units linked together (poly means “many”). Oligosaccharides contain between 2 and 10 sugar units (oligo means “few”). Glucose and fructose are two of the most common monosaccharides found in plants. Sucrose, found in sugarcane, is a disaccharide (di means “two”) formed by a link between the glucose and fructose.
Cellulose, the main component of plant cell walls and the most abundant organic compound on earth, is a homopolysaccharide—a compound made of chains of a single type of monosaccharide. Other important homopolysaccharides include starch, fructans, and inulins. These important dietary substances are commonly called complex carbohydrates.
Many other categories and subcategories of carbohydrates are found in plants and fungi. For example, myco-polysaccharides form the cell walls of mushrooms and are rich in fibrous carbohydrate substances called ß-D-glucans (pronounced beta-D-glucans), which have been studied for their immune-stimulating effects. Other ß-glucans are found in grains, including oats. They are an important source of soluble fiber.
Gums and mucilages—two other types of carbohydrates with various uses as food and herbal medicines—also consist largely of mono-saccharides. The term gum generally is understood to mean a sticky plant substance, such as gum arabic, made from black catechu (Acacia catechu). Mucilages are slippery substances used in herbal medicine to coat and soothe irritated or inflamed tissues (such as a sore throat). Marshmallow (Althaea officinalis), psyllium (Plantago ovata), and comfrey (Symphytum officinale) are all rich in slippery mucilage. Another important mucilage is carrageenan, derived from the Irish moss (Chondrus crispus), a seaweed, and from other species. Carrageenan is commonly used as a thickening agent in commercial food products.
EACH PLANT IS UNIQUE
Plants of the same species or even cultivar can vary in their plant chemistry, depending on their growing conditions and time of harvest. The compounds in St. John’s wort (Hypericum perforatum) thought to be responsible for its therapeutic activity can vary by as much as 50-fold in concentration, depending upon the season of harvest. Plant compounds can even vary on a daily basis. The chemical compound eugenol, when measured as a total concentration in the essential oil produced from a species of wild basil (Ocimum gratissimum), varied from 98 percent for a plant harvested at 12 a.m. to 11 percent for a plant harvested at 5 p.m. Researchers must consider these variations in concentration levels when testing an herb or herbal product in the lab.
Primary Metabolites: Lipids
Lipids—more commonly known as fats—are a major component of membranes in both plants and animals; they’re also found in various hormones, as well as in vitamins E and A. They serve as reservoirs of energy to fuel essential cell functions and, like carbohydrates, are building blocks for a range of secondary plant metabolites.
Among the most important plant lipids for human health and nutrition are fatty acids. Unlike the fats found in animal products, plant fats are rich in unsaturated fatty acids, which research shows are critical for heart health. The human body is capable of producing almost all fatty acid structures; however, some fatty acids cannot be manufactured by your body and therefore must be supplied through your diet. These fatty acids are of critical importance to human health and are called essential fatty acids.
The two essential fatty acids most closely linked to human health are omega-3 and omega-6. Although fish oils from tuna, mackerel, herring, and sardines may be the best sources of omega-3s, flaxseed (Linum usitatissimum) and the seeds of hemp (Cannabis sativa) contain omega-3 alphalinolenic acid, providing valuable nonanimal sources of essential fatty acids.
The seeds of flax (Linum usitatissimum) contain omega-3 fatty acids, as well as fiber and lignans—all important for health.
Primary Metabolites: Proteins
Proteins are large molecules with different but very important functions. Besides serving as structural components of cells and tissues, they also regulate biochemical processes in both plants and animals. In fact, every chemical reaction that occurs in living cells is controlled by a special type of protein called an enzyme.
Proteins are composed of hundreds of units called amino acids. There are about 20 different types of amino acids, and most plants can synthesize those necessary for survival. This isn’t the case for animals, which can synthesize only a few amino acids. For this reason, all animals—including humans—must obtain the missing, essential amino acids through their diets.
Vegetable proteins can be found in beans, nuts, and seeds, including peanuts (Arachis hypogaea), cashews (Anacardium occidentale), almonds (Prunus dulcis), walnuts (Juglans regia), sesame seeds (Sesamum indicum), sunflower seeds (Helianthus annuus), and soy beans (Glycine max).
Secondary Metabolites: Terpenes
Terpenes comprise the largest group of secondary plant metabolites. Thousands of different terpene compounds are found in a wide variety of plant species, and many appear to have important functions for the plants that produce them. For example, some give off aromas that lure pollinators or deter predators.
Terpene-rich volatile (essential) oils have great importance in herbal medicine and cooking. These aromatic compounds are responsible for the fragrances and flavors of kitchen favorites such as thyme (Thymus spp.), ginger (Zingiber officinale), peppermint (Mentha × piperita), and peel from citrus (Citrus spp.). These plants are not only tasty and aromatic, but they also have valuable antispasmodic, antimicrobial, and carminative (digestion-enhancing) effects.
Terpenes give us many other valuable medicinal compounds as well, including bitters, anti-inflammatory agents, expectorants, and sedatives. Limonene, a monoterpene found in citrus peel as well as mint, dill, and caraway, has been studied for potential cancer-preventive effects. Another important group of terpenes are the carotenoids—orange plant pigments found in oranges, peppers, and carrots—that the body converts into vitamin A.
Secondary Metabolites: Phenols
This group of plant chemicals includes thousands of different compounds that share one common chemical characteristic: All contain at least one phenol group. This is probably the largest group of plant secondary metabolites, and its compounds are widespread in nature. Plant phenols range from very simple structures to highly complex ones, such as tannins and lignins.
Green teas are rich in antioxidant polyphenols, powerful plant chemical compounds that are thought to protect your body against cell damage that can lead to cancer and heart disease.
THE A-TEAM: ANTIOXIDANTS
The term antioxidant seems to show up in nearly every health food claim and on every label—but just what does it mean? Antioxidant compounds defend your body against the effects of harmful chemicals called free radicals. Free radicals are unstable compounds that are products of oxidation in your body. Plant antioxidants are composed of a broad variety of substances that include phenols and some terpenes.
The human body produces free radicals in response to airborne pollutants such as cigarette smoke, stress, recreational drugs, food additives, and many other things. Free radicals can wreak havoc in your body, damaging cells and contributing to accelerated aging and a host of health problems, including serious conditions such as heart disease.
Antioxidants “scavenge” or “quench” free radicals to protect the human body against these harmful effects. Antioxidants are found in plants, especially fruits, vegetables, and herbs. Herbs that have particularly potent antioxidant actions include green tea (Camellia sinensis), milk thistle (Silybum marianum), turmeric (Curcuma longa), ginkgo (Ginkgo biloba), ginger (Zingiber officinale), garlic (Allium sativum), and horse chestnut (Aesculus hippocastanum).
At least half of all phenols are part of a large subgroup called flavonoids. Flavonoids contain many important antioxidant compounds that help eliminate harmful substances called free radicals from your body. The flavonoid category itself can be divided into numerous smaller subgroups of flavonoid compounds, including isoflavonoids, flavones, flavonols, flavonolignans, anthocyanins, and proanthocyanidins. When several phenol groups are attached to each other, the resulting compound is called a polyphenol.
Green tea (Camellia sinensis) is one of many phenol-rich plants with valuable health properties. It contains antioxidant phenols called catechins. Hundreds of studies conducted on these compounds suggest that they could help prevent cancer and heart disease. Many plants in the pea family (legumes) contain isoflavonoids, which also have demonstrated impressive cancer-fighting and hormone-balancing effects in modern studies. Plants rich in isoflavonoids include soy (Glycine max) and red clover (Trifolium pratense).
Many of the pigments that give plants their coloring are polyphenols. Antioxidant polyphenols called anthocyanins provide the blue and red colors of berries such as blueberries (Vaccinium angustifolium and others) and cranberries (V. macrocarpon). Red grapes (Vitis vinifera) and red wine contain anthocyanin pigments as well as resveratrol, another polyphenol. Studies have shown that berries and red wine, like green tea, could have healthful antioxidant effects.
Tannins are highly astringent polyphenols that can be used not only as tanning agents for the leather industry, but also as medicines. Astringents tone and tighten tissues throughout your body, including mucous membranes and skin; they are responsible for the mouth-puckering sensation you experience when drinking a cup of strong black tea. Oak bark (Quercus spp.), witch hazel (Hamamelis virginiana), and agrimony (Agrimonia eupatorium) are also rich in tannins.
Other important phenols include curcumin (found in turmeric, Curcuma longa), a powerful antioxidant that has anti-inflammatory and cancer-preventive properties, and silymarin, a mixture of flavonolignan compounds largely responsible for the health benefits of milk thistle (Silybum marianum). Modern studies have shown that milk thistle might protect your liver from the effects of toxins, including pharmaceutical drugs, and help it regenerate damaged cells.
CHEMICAL STRUCTURES in PLANTS
While the chemical structures of these secondary metabolites (terpenes, alkaloids, and phenols) appear very different, the compounds belonging to each of them could look similar to each other yet have completely different pharmacological activities.
The alkaloids caffeine and morphine, for example, have completely different pharmacological profiles even though their chemical structures are related. Each of these compounds is a psychoactive drug, acting on your central nervous system and affecting brain function. But while caffeine is a mild stimulant that’s widely consumed in coffee and teas, morphine, the major constituent of opium, is a powerful narcotic (sleep-inducing) drug used to treat and manage moderate to severe pain.
Secondary Metabolites: Alkaloids
This group of plant chemicals can have powerful effects in the human body. Many are potent medicinal compounds that can be toxic in high doses; others are highly addictive.
Caffeine, a naturally occurring stimulant and diuretic found in coffee (Coffea arabica), green tea (Camellia sinensis), and other foods, is one familiar alkaloid. Other potent alkaloids include ephedrine, a decongestant taken from ephedra (Ephedra sinica); theophylline, a bronchial smooth-muscle relaxant present in small quantities in tea; reserpine, a tranquilizer and antihypertensive made from the Indian serpentwood plant (Rauvolfia serpentina); and vincristine and vinblastine, cancer-fighting compounds made from Madagascar periwinkle (Catharanthus roseus).
Some alkaloids have hallucinogenic effects. Examples include mescaline, which is extracted from the peyote cactus (Lophophora williamsii), and psilocybin, which is found in mushrooms of the genus Psilocybe. Other alkaloids are highly addictive. They include cocaine, a stimulant and anesthetic taken from the leaves of the South American coca plant (Erythroxylum coca); nicotine, taken from the leaves of the tobacco plant (Nicotiana tabacum); and morphine, a pain reliever extracted from the opium poppy (Papaver somniferum).
Certain pyrrolizidine alkaloids, such as those found in plants of the borage family, including comfrey (Symphytum officinale), can cause liver damage. Other poisonous alkaloids include strychnine (found in Strychnos nux-vomica), atropine (found in Atropa belladonna and Datura stramonium), and coniine (a deadly toxin made from poison hemlock, Conium maculatum).
Phytochemists use the term glycoside to describe a plant compound that has a molecule of sugar attached to a noncarbohydrate molecule, called an aglycone.
Glycosides are particularly important in the study of herbal medicine. Many have important medicinal actions; others are dangerous toxins. The cyanogenic glycosides found in apple seeds and bitter almonds, for instance, produce the deadly poison cyanide. But the cyanogenic glycoside prunasin, found in wild cherry bark, is an expectorant when taken in small quantities.
Cardiac glycosides, such as those in lily of the valley (Convallaria majalis) and foxglove (Digitalis spp.), are extremely potent chemicals that should never be taken during self-treatment. Cardiac glycosides improve your heart’s efficiency without increasing its need for oxygen. Plants containing these compounds were once the only treatments for serious heart conditions, such as congestive heart failure (a disease in which your heart loses its ability to efficiently pump blood). However, because cardiac glycosides are eliminated from your body slowly, dangerous levels can accumulate in your blood. To treat congestive heart failure today, doctors prescribe modern pharmaceuticals such as digoxin (isolated from Digitalis lanata), which they can monitor and control the dosages of more easily.
Another group of glycosides are the glucosinolates, found primarily in cruciferous vegetables (members of the mustard family, Brassicaceae) such as broccoli, cabbage, and kale (all Brassica oleracea), horseradish (Armoracia rusticana), mustard (B. nigra and others), and radish (Raphanus sativus). When one of these plants is crushed, its glucosinolates undergo a chemical reaction that creates the volatile oil compounds we know as mustard oils. When applied to the skin, mustard oils have a warming, stimulating effect—that’s why mustard poultices were traditionally used to relieve chest congestion. Research has shown that indole-3-carbinol might help prevent certain cancers, including colon and breast cancers, and indole-3-carbinol is produced in your body as you break down the glucosinolates in cruciferous vegetables.
Catharanthus roseus, the source of the chemotherapeutic drugs vincristine and vinblastine.
NATURE’S MEDICINE CHEST
Contemporary medical care is filled with new and exciting technologies and approaches. Reports of great advances in our understanding of illness and its treatment appear in scientific journals, newspapers, and other media on a weekly, and sometimes daily, basis. From time to time, reports also appear about the empty pipelines in drug discovery programs, when expectations fueled by modern technology have not been met. Yet many of these programs overlook a rich source of potential therapies—the plant world.
What role could nature, specifically plants, play in contemporary medicine? Some write about the obsolescence and dangers of using plants in healing, while others suggest that the “well” of plants that could be used to improve both health care and the outcomes of disease is far from dry. James S. Miller, PhD, noted in a recent issue of the journal Economic Botany that 135 pharmaceutical drugs have been discovered from plants to date and, based on his analysis of the world’s flora and conservative historic drug discovery rates, he projects that at least 500 more pharmaceutical drugs remain to be discovered. Delaying the progress toward improved health-care options and outcomes is the fact that as many as 70,000 plant species have yet to be discovered and, because of habitat destruction and other consequences of global change, many species could disappear before they are identified and evaluated for their chemical composition and medicinal potential.
Here are a few facts to consider. As Dr. Miller points out, many of our most important prescription pharmaceuticals are based on single compounds derived from plants. For example, the compound vincristine, derived from the rosy periwinkle (Catharanthus roseus) and approved for use by the FDA in 1963, is used to treat the 3,800 new cases of childhood leukemia diagnosed annually in the United States. It has an impressive record of up to 90-percent remission, based on the type of cancer and age of the patient. A relatively recent example of a whole plant extract being developed as an effective pharmaceutical is from a plant familiar to all—tea (Camellia sinensis). In 2006, the FDA approved the prescription use of a topical preparation of tea extract for the treatment of perianal and genital condyloma (warts). When applied as an ointment, Veregen, as this pharmaceutical is called, completely resolved these conditions in 54 percent of patients who used it.
Many herbal remedies prepared as whole-plant extracts and sold as supplements, tinctures, or teas are being incorporated into Western health care through the field of integrative medicine, which is now taught at more than 50 academic medical centers and affiliate institutions in the United States alone. Clinical and preclinical research of these plants and their compounds is underway, and those herbs and formulations with convincing evidence of safety and efficacy will continue to find their way into Western medical care.
Meanwhile, much of the developing world still depends on plants to treat many primary health-care conditions—ranging from respiratory infections, wounds, and colds to diarrheal diseases that could otherwise prove fatal. Nature is the medicine chest for billions of people, and many generations of their traditional healers—the equivalent of our Western physicians—have already carried out human clinical trials.
It turns out that Mother Nature is a brilliant chemist. Hundreds of thousands of compounds have been identified from plants. Some of these are used in prescription pharmaceuticals, others in botanical supplements, and many more remain to be discovered.
UNDERSTANDING HERBAL ACTIONS
Long before scientists began to study how herbs work, traditional healers discovered herbal actions empirically. They used intuition and observed how animals use plants to heal themselves. They experimented, then verified and documented what they learned so that their knowledge could be passed along.
These hands-on healers—folk doctors and village healers, shamans, monks, and nuns, all serving their communities—are the ones to thank for many so-called scientific discoveries about herbs. The indigenous people of northeast Brazil, for example, have long used the jaborandi plant (Pilocarpus jaborandi) for medicinal purposes, including the promotion of salivation. Pilocarpine, a pharmaceutical medicine developed from this species, has been used worldwide to treat glaucoma and other conditions. Most recently, it was approved for the treatment of “dry mouth syndrome,” which can be a side effect of radiation therapy or certain health conditions. And while laboratory research shows that garlic (Allium sativum) has antimicrobial activity, traditional healers knew this through experience and have long used the herb to treat all kinds of infections, from colds and flu to infected skin wounds.
Feverfew (Tanacetum parthenium) is best known for helping prevent migraine headaches, but it has also been used to treat arthritis, dizziness, tinnitus, and painful menstruation.
One way to learn how to use medicinal herbs is to learn about their possible effects on the human body. Much like modern pharmaceuticals, herbs can have antispasmodic (muscle-relaxing), analgesic (pain-relieving), and anti-inflammatory effects. Other herbal actions are described with unique terms such as adaptogenic (helping the body defend against physical stress), alterative (slowly restoring efficient body function), and carminative (enhancing digestion).
Herbs appear to have what herb researchers call “affinities” to particular body systems; in other words, herbal actions are more pronounced in some parts of the body than others. Among demulcent (inflammation-relieving) herbs, corn silk (Zea mays) comforts the urinary tract, while marshmallow root (Althaea officinalis) soothes the digestive tract. Kava (Piper methysticum) is an antispasmodic that relaxes muscles all over the body, while wild cherry bark (Prunus serotina) acts primarily to relax respiratory muscles. Hawthorn (Crataegus laevigata) strengthens the heart and blood vessels, while raspberry leaf (Rubus idaeus) tones the tissue of the uterus.
In addition, even though an herb can be especially well known for a certain effect (and so is termed a “specific” for a particular condition), most herbs provide a combination of actions. German chamomile (Matricaria recutita), for example, is known as a specific for the treatment of stomach ulcers because it has an anti-inflammatory effect on the digestive tract. It also soothes frazzled nerves, relaxes tense muscles, alleviates indigestion, and is a valuable anti-inflammatory remedy for skin irritations. Feverfew (Tanacetum parthenium) is best known for helping prevent migraine headaches, but it has also been used to treat arthritis, dizziness, tinnitus, and painful menstruation or sluggish menstrual flow.
In other words, from a therapeutic perspective, herbs have both primary and secondary actions. By considering the primary and secondary actions of herbs, as well as their body-system affinities, an herbalist can choose an herbal treatment appropriate not only for relieving an acute problem, but also for improving chronic conditions or heading off future problems.
Catnip (Nepeta cataria), for instance, is an antispasmodic herb that also relieves indigestion and acts as a mild sedative, so it’s an excellent choice for someone who suffers from stress-related indigestion. And garlic (Allium sativum), which relieves infections and aids the circulatory system, could benefit someone who has bronchitis as well as a family history of heart disease.
THE TWO FACES of PURPLE CONEFLOWER
Current knowledge about the chemistry and pharmacology of purple coneflower (Echinacea purpurea) helps show why an herb can have multiple effects on the body. We’ve discovered that a plant’s pharmacological effect depends not only on the chemicals present in the herbal preparation, but also on the different targets of a particular chemical.
Purple coneflower has long been used to prevent and treat the common cold. Traditionally, echinacea preparations were made from roots, but more recently, producers have been using the fresh-pressed juice from the flowers. While analyses of the plant’s bioactive constituents are far from complete, scientific studies have consistently shown that different compounds in echinacea preparations stimulated the immune responses of animals—humans included—to viral infections, supporting the traditional use of this herb.
But recent scientific findings show that echinacea preparations could also inhibit some immune cells, possibly adjusting the immune response to an appropriate level. This can be a benefit, since an excess of some immune-regulating chemicals (known as cytokines) in your body after a viral infection can be detrimental to your health.
The bioactive constituents of Echinacea purpurea include alkamides, phenolic compounds, polysaccharides, and glycoproteins, among others. In general, alcoholic tinctures contain higher levels of alkamides and phenolic compounds, while aqueous extracts contain more polysaccharides and glycoproteins. In terms of pharmacological activities, polysaccharides and glycoproteins have been identified as having immune-stimulating activity, while alkamides appear to be anti-inflammatory. Phenolic compounds could work both ways.
While studying the effect of Echinacea purpurea on T lymphocytes, a type of white blood cell that fights virus and cancer cells, I found that some of the polysaccharides in the flower tops were able to not only increase, but also decrease the amounts of some cytokines released during a viral attack. Some of our tests suggest that this polysaccharide would be more effective if the preparation were taken before or during the early stage of a viral infection, validating clinical data as well as traditional wisdom about the benefits of early use of echinacea as a plant medicine.
—Fabiana N. Fonseca, PhD
Tonics and Effectors
Medicinal herbs can be grouped roughly into two very broad categories, according to the intensity of their activity: tonics and effectors.
Tonics are mild herbs that can be taken over the long term as preventive medicines or to gently correct and balance body functions. These herbs, which are more like foods than medicines, are among the safest of plant remedies. Nettle (Urtica dioica) is a general tonic herb. Like all herbs, tonics display affinities for particular body systems. For example, hawthorn (Crataegus laevigata) and garlic (Allium sativum) are excellent tonics for the cardiovascular system, while bitter herbs, such as mugwort (Artemisia vulgaris), are effective for the digestive system.
Effectors, on the other hand, have a more immediately noticeable effect upon your body. Herbalists call on these herbs to treat acute illnesses (such as infections) and relieve specific symptoms (such as a cough or sore throat). While many effectors are mild and can even be used as tonics, others contain powerful chemical constituents and must be used with caution. Some can even be toxic in high doses.
Mild effector herbs include feverfew (Tanacetum parthenium), saw palmetto (Serenoa repens), and turmeric (Curcuma longa). Strong effectors include stimulant laxatives such as senna (Senna alexandrina) and buckthorn (Rhamnus cathartica), as well as powerful, potentially toxic herbs, such as lobelia (Lobelia inflata), which some herbalists use in minute doses to relax muscles in people suffering from asthma and bronchitis, and poke-weed (Phytolacca americana), which is occasionally used in small doses to treat infection and promote lymphatic drainage.
Synergistic, Additive, and Antagonistic Effects of Herbal Extracts
When herbs are combined in mixtures or formulas, the chemical characteristics of the overall mixture can change, increasing or decreasing the availability and effects of some of the constituents.
Traditional Chinese medicine (TCM) combines herbs within formulas, taking into consideration the synergistic, additive, and antagonistic effects among the constituent herbs. This practice is also common in other herbal systems, such as in Central and South America, where many health conditions are treated with bottled herbal mixtures called botellas (in Spanish-speaking countries) or garrafadas (in Portuguese-speaking countries).
Advancements in analytical and synthetic chemistry now make it possible to better understand the potential effects of drug combinations on a living system. Scientists are exploring the dose-effect relationships (the change in effect caused by different dose levels) of each drug alone and in combinations to determine whether a given drug or herbal mixture would have an additive, synergistic, or antagonistic effect.
An additive interaction means that the effect of two chemicals taken together is equal to the sum of the effect of the two chemicals taken separately. Synergism, on the other hand, implies an effect that is more than additive—taken together, the two herbs have a greater effect. And antagonism is an effect that is less than additive—taken together, the herbs have a lesser effect.
A combination of herbs in a formula or mixture can target multiple areas of your body and a variety of conditions simultaneously. What’s more, combining multiple herbs that have different mechanisms of action also can provide more effective treatment against a disease.
In the Dominican Republic, a traditional herbal preparation known as a botella contains different plant parts immersed in alcohol. The beverage is used to prevent and treat many health conditions.
Because of these plant interactions, herbal preparations offer several advantages: They can increase the efficacy of the therapeutic effect; they can reduce the chance of toxicity because less of each herb is needed to achieve the same result; and they can minimize or slow the development of drug resistance.
Addition and antagonism can also be used to perfect an herbal formulation. In a 2006 Yale Scientific article outlining the importance of integrating Western and Eastern medical practices to address unmet needs in “conventional” medicine, Yung-Chi Cheng, a professor at Yale Medical School, explained the interaction and roles of different herbs in TCM using the following metaphor:
The herbs in a typical TCM formulation . . . play different roles. Jun, the emperor herb, is the principal ingredient; chen, the minister herb, aids the jun often by augmenting or broadening its effects or by attending to secondary symptoms; zuo, the assistant, can moderate the activities of the jun and chen or also address secondary symptoms; finally, shi, the ambassador herb, aids in the absorption and transport of all the other herbs to their destinations. Thus, the herbs prescribed in a given formulation must work in concert to achieve a desired effect.
Just as herbs can interact synergistically or antagonistically when combined, so can herbs and pharmaceutical drugs. For example, one in four people in the United States over 45 years of age takes statins, a class of pharmaceutical drug used to lower blood cholesterol levels. Statins work by inhibiting an enzyme that produces cholesterol in your body, so they are considered important in reducing heart disease. The statins are broken down by another enzyme system in your body, leading to their elimination.
But bergamottin, a compound in grapefruit, can block the process that breaks down statins, allowing them to build up to levels that can quickly become toxic, resulting in severe liver, kidney, and muscle damage. That’s why physicians advise their patients not to consume this fruit or its juice while taking statins. Now researchers are considering the possibility of using grapefruit compounds to increase the amount and effects of certain drugs in the body so that smaller amounts of these drugs can be used.
Ginkgo (Ginkgo biloba) dilates blood vessels, which helps with cardiovascular conditions, such as high blood pressure. Adverse effects could occur when combining ginkgo with other antihypertensive or certain antidepressant drugs.
In a recent preliminary study, a patient who drank a single 8-ounce glass of grapefruit juice daily increased the absorption of a specific chemotherapeutic drug by up to 350 percent. While much further research is necessary, the study suggests that drugs modulated by plant compounds, such as those found in grapefruit, could be prescribed in smaller amounts.
Many herb-drug interaction charts can be found online. While there are many potentially problematic herb-drug interactions, scientific data has shown that most (but not all) commercially produced herbal products, as well as the herbs themselves (except, of course, for the toxic species) are generally safe when used under the supervision of a knowledgeable health-care practitioner.
The extraordinary chemical diversity of herbs has remarkable potential to improve human health and well-being. To achieve this potential, rigorous clinical trials under standardized, reproducible conditions are needed. Pilot experiments—small-scale clinical trials with herbs and patients—can provide guidance for the design of larger studies. The gold standard for evaluating any new therapy—drug or herb—is the randomized, blind, placebo-controlled clinical trial, where participants are randomly placed into groups receiving the treatment or placebo and they do not know which of the treatments they are receiving. These types of studies will allow medical researchers to determine which herbs are effective for treating specific health conditions and which ones could help us stay healthy as we age, and—of equal importance—which herbs lack sufficient evidence of safety or efficacy, and which might interfere with the proper action of the pharmaceutical drugs we take.
In many ways, medicine is returning to its original roots: using plants to improve the quality of our lives.
A GLOSSARY of HERBAL ACTIONS
Many terms are specific to the practice of herbal medicine. The terms on the following pages are not a comprehensive list of herbal actions, but are meant to help explain a few of the basic terms associated with Western herbalism. Other systems, such as traditional Chinese medicine (TCM) and Ayurveda, which are based on completely different concepts, have a terminology all their own. (See this page and this page for more on these healing systems.)
Adaptogens are compounds found in herbs that can help your body adapt to and defend against the effects of physical stress, such as extreme cold or sleep deprivation. Scientists do not yet understand exactly how adaptogens work. Some theories suggest that they may help control the release and effects of stress hormones and modulate blood glucose levels, which in turn counteracts the damaging effects of stress on your body. Common adaptogenic herbs are ginseng (Panax spp.), eleuthero (Eleutherococcus senticosus), and reishi mushroom (Ganoderma lucidum).
Alteratives are herbs used to gradually bring about fundamental changes in health. Often, they are used to treat chronic skin conditions or autoimmune diseases. Researchers are unsure of how they work, but scientific studies offer a number of possibilities. Some alteratives, such as burdock (Arctium lappa), nettle (Urtica dioica), and yellow dock (Rumex crispus), seem to improve the efficiency of basic body functions, such as digestion, assimilation of nutrients, and elimination of wastes. Others, such as echinacea (Echinacea spp.), benefit your immune system. As with many herbs, alteratives probably work by a combination of effects.
Analgesics and anodynes are pain relievers. Examples include willow bark (Salix spp.), poplar (Populus spp.), and devil’s claw (Harpagophytum procumbens).
Anticatarrhal herbs help your body eliminate excess mucus. Many of these herbs contain astringent tannins; others are rich in volatile oils. Examples include elecampane (Inula helenium), hyssop (Hyssopus officinalis), and thyme (Thymus spp.).
Anticholesterolemic herbs, such as green tea (Camellia sinensis), lower cholesterol levels by either inhibiting your body’s production or absorption of cholesterol or by enhancing its excretion.
Anti-inflammatory agents reduce swelling and redness associated with inflammation. Anti-inflammatory herbs for internal use include turmeric (Curcuma longa), meadowsweet (Filipendula ulmaria), wild yam (Dioscorea villosa), and devil’s claw (Harpagophytum procumbens). Anti-inflammatory herbs used externally include St. John’s wort (Hypericum perforatum) and arnica (Arnica montana).
Antimicrobial herbs contain compounds that kill pathogens, or disease-causing organisms. Herbs with antibacterial, antifungal, and antiviral actions are all considered antimicrobial. Some antimicrobials, such as echinacea (Echinacea spp.), also stimulate your immune system. Research has shown that cranberry (Vaccinium macrocarpon) and related plants can prevent urinary tract infections because they discourage the attachment of bacteria to the walls of your urinary tract.
Antioxidants protect your body from the damaging effects of free radicals and may help protect against various degenerative diseases. (See “The A-Team: Antioxidants.”)
Antirheumatic herbs are helpful in the treatment of arthritis and other degenerative conditions that affect connective tissue. These herbs include devil’s claw (Harpagophytum procumbens), turmeric (Curcuma longa), nettle (Urtica dioica), boswellia (Boswellia serrata), and feverfew (Tanacetum parthenium).
Antispasmodic herbs relax muscles and ease muscle spasms and cramps. Some may alleviate muscle tension throughout your body, while others are specific to certain types of muscle tissue or organ systems. Many are also relaxing nervines, easing psychological tension as well. Chamomile (Matricaria recutita) and valerian (Valeriana officinalis) relax spasms in your digestive tract and calm nervous tension. Mullein (Verbascum thapsus) relieves spasms in your respiratory tract. Valerian helps ease muscle tension throughout your body.
Astringents tighten and tone tissues, especially mucous membranes, usually due to their tannin content. They also help dry excess secretions. They can be taken internally to treat conditions such as diarrhea or externally, as styptics, to stop bleeding. Examples include yarrow (Achillea millefolium) and witch hazel (Hamamelis virginiana).
Bitter herbs stimulate digestion, enhancing the flow of digestive juices and peristalsis, the muscle action that moves food through your digestive tract. Some bitter salad greens are eaten before a meal to aid digestion. Gentian (Gentiana lutea), mugwort (Artemisia vulgaris), and dandelion leaf (Taraxacum officinale) are bitter herbs.
Carminative herbs relieve gastrointestinal stress. They also enhance peristalsis, the action that moves food and gas through your digestive tract. Many are also popular culinary herbs and spices; those include thyme (Thymus spp.), dill (Anethum graveolens), caraway (Carum carvi), and ginger (Zingiber officinale).
Cholagogue herbs act by stimulating the flow of the digestive enzyme bile, which aids the digestive process. Dandelion root (Taraxacum officinale) is a cholagogue.
Demulcent herbs soothe and protect irritated or inflamed tissue and are often specific to one or more body systems. For instance, marshmallow leaf (Althaea officinalis) is a urinary tract demulcent; marshmallow root and licorice (Glycyrrhiza glabra) are digestive system demulcents. Respiratory demulcents include mullein (Verbascum thapsus), licorice, and marshmallow root.
Diaphoretic herbs induce perspiration, helping to “break” a fever and improve circulation. They’re also used to treat colds and flu. Examples include yarrow (Achillea millefolium), boneset (Eupatorium perfoliatum), and ginger (Zingiber officinale).
Diuretic herbs stimulate the flow of urine and help your body eliminate excess fluid. Some also have antiseptic actions in your urinary tract, making them useful for urinary tract infections. These could be too irritating for people with kidney problems, however. Examples include dandelion leaf (Taraxacum officinale), parsley (Petroselinum crispum), and saw palmetto (Serenoa repens). Juniper (Juniperus communis) is a diuretic with strong antiseptic properties.
Emmenagogue is a term that once referred to herbs that induced menstrual flow, but it has come to be used more loosely to describe herbs that benefit female reproductive health. Herbs thought to stimulate sluggish menstrual flow include yarrow (Achillea millefolium) and feverfew (Tanacetum parthenium). Black cohosh (Cimicifuga racemosa) and vitex (Vitex agnus-castus) are believed to help normalize the function of the female reproductive system.
Expectorant herbs promote the elimination of mucus from your lungs. Stimulating expectorants, which commonly contain volatile oils, saponins, or alkaloids, include horehound (Marrubium vulgare), elecampane root (Inula helenium), and mullein leaves (Verbascum thapsus).
Galactogogue herbs help stimulate the flow of milk in nursing mothers. Galactogogues include dill (Anethum graveolens) and fennel (Foeniculum vulgare). Both are also classic remedies for infant colic.
Hepatic herbs help improve liver function. Examples include milk thistle (Silybum marianum) and licorice (Glycyrrhiza glabra).
Hypnotic herbs induce sleep and can be taken to treat insomnia. Examples include hops (Humulus lupulus), valerian (Valeriana officinalis), and passionflower (Passiflora incarnata).
Hypotensive herbs help lower blood pressure. These include hibiscus (Hibuscus sabdariffa), hawthorn (Crataegus laevigata), and valerian (Valeriana officinalis).
Immunomodulator herbs affect immune function. Some, such as echinacea (Echinacea spp.), stimulate immune cells such as phagocytes, which fight infection by destroying invading pathogens. (See “The Two Faces of the Purple Coneflower.”) Others are the subjects of ongoing clinical research to determine and clarify their activity. Among these herbs are astragalus (Astragalus membranaceus), shiitake mushroom (Lentinus edodes), and reishi mushroom (Ganoderma lucidum).
Laxative herbs stimulate the action of your bowels. Bulk-forming laxatives are high in fiber; they include psyllium (Plantago ovata) and flaxseed (Linum usitatissimum). Stimulant laxatives chemically induce peristalsis; they include senna (Senna alexandrina), cascara sagrada (Rhamnus purshiana), and buckthorn (R. cathartica). High doses of these laxatives are not recommended for long-term use. Mild laxatives that work through other actions (by stimulating bile flow, for example) include dandelion root (Taraxacum officinale) and yellow dock (Rumex crispus).
Nervine herbs affect the function of your nervous system. Nervines can be relaxing, tonic, or stimulating. Relaxing nervines include valerian (Valeriana officinalis), passionflower (Passiflora incarnata), and chamomile (Matricaria recutita). Tonic nervines include oats (Avena sativa) and St. John’s wort (Hypericum perforatum). Herbs that stimulate your nervous system include caffeine-containing plants, such as tea (Camellia sinensis), as well as volatile oil–rich plants, such as rosemary (Rosmarinus officinalis) and peppermint (Mentha × piperita).
Rubefacients are herbs that, when applied externally, draw blood to an area for a localized warming effect. They include ginger (Zingiber officinale), black mustard (Brassica nigra), and chile pepper (Capsicum annuum).
Vasodilator herbs dilate blood vessels, which is useful in the treatment of cardiovascular conditions such as high blood pressure. Examples include ginkgo (Ginkgo biloba) and feverfew (Tanacetum parthenium).
Vulnerary herbs speed the healing of wounds. Examples include aloe (Aloe vera), comfrey (Symphytum officinale), calendula (Calendula officinalis), and St. John’s wort (Hypericum perforatum). Some vulnerary herbs can also be used internally.