Nature's Pharmacopeia: A World of Medicinal Plants
Valerian is an herbaceous perennial native to Europe and Asia, now naturalized in North America. While there are over 200 species in the genus Valeriana, a number of which have been used medicinally, the type with the longest history and most widespread interest is probably V. officinalis.176 The plant consists of a stem that reaches 2 meters in height, with leaves composed of many narrow, oval green leaflets and clusters of tiny pink or white flowers. The underground portion of the plant, made up of rhizomes, stolons, and roots, is harvested for its ascribed health-related properties (figure 14.23).177
Documented as a medicinal plant as early as the writings of the Greek Hippocratic physicians and elaborated by authorities including Dioscorides and Galen, valerian has long been recognized for diverse therapeutic applications.178 For example, in his De materia medica (ca. 60 C.E.), Dioscorides recommended that the root be prepared as an herbal tea to promote urination, treat pain in the sides, and “[draw] down the menses.” He categorized the herb as warming and noted that its medicinal potency was revealed by the rather unpleasant smell of the dried root.179 In 1597, the English physician John Gerard listed valerian root to treat urinary problems, jaundice, and “slight cuts, wounds, and small hurts.” A liquid extract of the leaves, he wrote, was useful as a mouthwash or gargle to treat sore mouth and gums.180 Several decades later, the popular herbalist Nicholas Culpeper outlined more than a dozen treatments involving valerian on its own and in combination with other substances, recommending it to cure coughs, expel phlegm, improve eyesight, and remove thorns and splinters. In an era when periodic epidemics of infectious disease threatened the urban areas of Europe, Culpeper offered the helpful hint: “It is of special Vertue against the Plague,” the foul odor of the root being repulsive to pestilence.181
FIGURE 14.23 Valerian: (left) flowers; (right) root.
Valerian’s reputation gradually shifted toward a role in behavior and affect, and doctors recommended it for ailments (in nineteenth-century terms) such as hysteria, hypochondria, and chorea (tremors).182 The English medical self-help book The Working Man’s Family Botanic Guide (1852) called valerian “a nervine, and antispasmodic,” useful to treat “nervous diseases.”183 By the twentieth century, valerian was less widely employed in medicine than previously but was known in informal medicine as a relaxant and sleep aid, particularly in Europe.184
The chemical profile of valerian root is highly variable, dependent on growing conditions and processing techniques. The constituents thought to be responsible for medicinal effects are volatile oils (0.2–2.8 percent in the root), including the compound valerenic acid (figure 14.24).185 Laboratory studies have demonstrated that valerenic acid and a closely related chemical from valerian can bind to, and enhance the activity of, a receptor for the neurotransmitter GABA.186 Since GABA inhibits certain types of excitatory signals in the central nervous system, valerian extract is proposed to act as a calming agent. This hypothesis has been investigated in tests of anxiety in laboratory rats, and evidence is mounting that valerian extracts have such a property.187 Clinical trials have sought evidence for anxiolytic effects among volunteers with anxiety or insomnia, and the results of such experiments are mixed. Reviewers of the clinical studies involving valerian have noted the diverse testing schemes, dosing, and source of valerian extract, along with other methodological concerns that (so far) obscure a conclusive interpretation of outcomes.188
FIGURE 14.24 Valerenic acid.
With a long history in European medicine as a potent, though malodorous, herb, some of valerian’s effect has now been described in neurochemical terms. Whether or not large-scale human trials of valerian extract yield definitive evidence of a calming effect in human beings, knowledge of valerenic acid’s unique activities in the brain can shed new light on the basic circuitry of the nervous system, ultimately yielding a wealth of information for which modern science would have nature and generations of traditional medical practitioners to thank.