In their search for nourishment, primitive humans sampled many kinds of plants. Those that were palatable were used for food, while plants with toxic or unpleasant effects were avoided or used against enemies. Still other plantsÑthose that produced physiological effects such as perspiration, defecation, healing, or hallucinationsÑwere saved for medicinal purposes and divination. Over the course of thousands of years, people have learned to use a wide variety of plants as medicines for different ailments.
Use in Modern Medicine
The widely held belief that modern medicines are all the product of complex chemical syntheses is a fallacy. More than 120 current prescription drugs are still obtained from higher plants, resulting in sales exceeding $12 billion annually in the United States alone, and about 25% of all prescriptions contain one or more active ingredients from plants. Indeed, pharmaceutical firms that once shunned natural-products research are now beginning to study the possibilities of this resource. Around the world, numerous companies have been formed to explore the potential of plants as modern medicines.
Many names could be cited of plants, long in use by indigenous peoples, that have found their way into modern medicine. One can serve as an example: Pilocarpus jaborandi, a shrubby tree of northeastern Brazil that is the source of pilocarpine, a compound used to reduce the interocular pressure resulting from glaucoma. In Brazilian folk medicine it was originally used to increase salivation and cause swelling. The leaves were introduced into Europe in 1873, and by 1877 the compound pilocarpine, isolated from the leaves, began to be employed in ophthalmology. More recently the drug has also been approved, by the U.S. Food and Drug Administration, for the treatment of dry-mouth syndrome (a side effect of certain cancer treatments and a disease of aging). Recent domestication of Pilocarpus species as crop plants is taking the pressure off the wild sources.
Not all plant-derived drugs have backgrounds in traditional and folk medicine. Some of them have instead been developed as the result of a broad-scale, random search of the plant kingdom. One example is the discovery of taxol, which is derived from the bark of the Pacific yew, Taxus brevifolia. Recently introduced into the war on cancer, this drug is now usedÑeither alone or in combination with other therapiesÑfor the treatment of breast and ovarian cancer.
Current Problems and Prospects
As new screening systems are developed, even well-known plants are subjected to reanalysis in hopes of identifying new pharmacological actions.
Even so, fewer than one percent of the world's known 265,000 species of higher plants have as yet been exhaustively examined for their chemical composition and medical potential. The pharmacological search of the balance of the plant kingdom is truly a race against time, as deforestation and species extinction, coupled with the loss of knowledge about the traditional medicinal uses of plants, are reducing this vast phytochemical reservoir with increasing speed.
The maintenance of natural areas where so many medicinal plants are found is an important objective of conservation activities, since large numbers of people depend on the availability of these species for their primary health-care needs. In some countries such as Belize and India, forest reserves devoted to the conservation and utilization of medicinal plants have been established, often by local governments. In addition, there is a growing recognition of the economic value of traditional medicines and their importance to local people in many developing countries. These factors have been important in promoting the establishment of protected areas for medicinal plants.
Finally, in countries such as the United States, there is significant interest in alternative medicine. Up to a third of the population reports some involvement in herbal remedies and other such therapie. Clinical studies with plant extracts are being initiated, and the results with many species are encouraging. For example, the prickly pear cactus, Opuntia ficus-indica, has been studied for use by patients with benign prostatic hypertrophy, a disease found in middle-aged and older men. Dried flowers of the species were given to patients, and results were so promising that further clinical trials are now under way. Many plants deserve evaluation for clinical application in modern medicine. This appears to be a promising direction for future studies aimed at improving human health.