What the Leaves Can Tell Us

How a walk in the woods might lead to a medical breakthrough

| May/June 2001


More than 40 percent of all prescriptions filled are derived from plants and other organisms.

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Larry Dossey, M.D.


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affair with herbs; in 1998 we spent about $4 billion on herbal medicine and supplements. The phenomenal rise of herbal and other holistic forms of healing at the end of the 20th century stands as one of the chief symbols of modern civilization’s reawakening green consciousness.

The herb that took first place in health-store sales in 1998 was Ginkgo biloba, which comes from the leaves of the ginkgo tree. Ginkgo is an ancient plant. It has been around for 200 million years and is considered by botanists to be something of a living fossil. The main reason people consume ginkgo is to perk up their cognitive powers and memory. Is it merely coincidental that a tree whose genetic memory reaches back 2 million centuries is being used to treat our memory problems? It’s as if the ginkgo tree is saying, "Hey, I’ve been around for a very long time and I’ve got this memory thing down pat. Want some help?"

I believe that we are in communication on some level with plants and animals, which helps us discover—and rediscover—how we can use specific plants for certain maladies.

Biologist Lyall Watson, for instance, has studied how traditional healers and plants interact on the island of Madagascar. "Humans are very new there," he writes in Jacobson’s Organ, "having arrived only in the last two thousand years to confront an exotic flora of almost 15,000 species of flowering plants, 90 percent of which were totally unfamiliar to the immigrants from Africa and Asia. And yet these newcomers have managed to compile an impressive pharmaco-poeia of useful herbal remedies, thousands of which are on sale in every country market. There just hasn’t been time to test every strange plant on the island and decide which part, of which species, picked in which season, and prepared in which way, would be appropriate for which human condition. . . . They must have had help."

The help, it seems, comes from the plants themselves. When Watson asked traditional healers how they know that an extract from the leaves of a local flowering plant, picked in the spring, is good for what they call "milky blood," he always gets the same answer. "Oh, it’s easy," they say, "we ask the plants."

"A healer with a problem goes out into the forest, thinking about the patient, and tries to sniff out a solution by wandering, with an open mind, until something stops him, until a particular plant catches his attention and gives a whole new slant to the idea of an elective procedure by offering itself as a remedy," Watson explains.

Watson was skeptical until he discovered that the condition the local healers call "milky blood" is leukemia, and the plant the healers chose for use is a lovely pink flower called the Madagascar periwinkle, from which a major pharmaceutical company extracts the drugs vincristine and vinblastine, used to treat certain types of leukemia.

We’d better listen up. As noted Harvard biologist E.O. Wilson points out, "Few are aware of how much we already depend on wild organisms for medicine. In the United States a quarter of all prescriptions dispensed by pharmacies are substances extracted from plants. Another 13 percent come from microorganisms and 3 percent more from animals, for a total of over 40 percent that are organism-derived." Even the National Institutes of Health, the massive federal research institution, has begun working closely with herbal healers in many countries to identify new drugs, and drug giant Bristol-Myers Squibb has made deals with native healers in Asia to look for native plants.

How do indigenous healers know what the plants are saying to them? The trick, they say, is learning how to listen without censoring or getting in the way. This method takes on a new meaning in the study of chimpanzees. Researchers inspired by chimpanzee specialist Jane Goodall have found that chimps swallow single, whole leaves from any of 34 different trees. The leaves emerge intact and undigested in the dung. This habit peaks about two months into the rainy season, which is also peak time for infection with a major intestinal parasite. Observing the chimps, Michael Huffman of Kyoto University discovered that only sick chimps swallow the leaves. All the leaves, he finds, have bristles on their undersides. When researchers examined the defecated leaves, live worms were found caught among the hairs and folds. Huffman’s theory is that the leaves pass through the intestine, snag the worms, and shuttle them out of the body.

Huffman also discusses watching a parasite-ridden, constipated chimpanzee in western Tanzania. Huffman saw the chimp reach for the shoot of a noxious tree that chimps usually avoid, peel it, and eat its bitter pith. Within 24 hours, all of its symptoms had vanished. It was the first time a scientist had seen a sick chimp select an unsavory plant known by humans to have medicinal properties, consume it, and then recover. One of Huffman’s key discoveries is that the pith the chimps eat contains around 20 compounds that have different levels of activity and exert different effects on intestinal parasites. "Some of the most bioactive compounds," he says, "act to paralyze the worm, inhibit movement, prevent egg laying. Other compounds are toxic [to the parasite]."

In modern medicine, we have opted for the magic bullet approach—the single-drug, single-action method to totally eradicating a pathogen. This promotes drug resistance, because the single mechanism stimulates the pathogen to develop a counterstrategy. In contrast, reports journalist Aisling Irwin, "Forest remedies rarely expunge the disease entirely; they just suppress it. The leaf-swallowing chimps still carry parasites, but in low, safe numbers. At the end of the rainy season, infections disappear naturally."

Opponents of herbal medicine disagree with this approach, sometimes with good reason. In some diseases such as AIDS, even a trace of the virus can infect others. But many of these same opponents miss one of the key principles of herbal medicine: Multiple compounds act synergistically. They assume that there is one key compound in the herb that can be isolated, synthesized, and used in pure form. Yet research like Huffman’s suggests that herbs may work because of the sheer variety of the substances they contain, not because of any single compound.

The critics of herbs are correct about one thing, however: There are hazards to green medicine. Some herbal preparations are toxic, which it would be foolish to ignore. But the current debate about the dangers of herbs often becomes overheated and unbalanced, especially in view of the fact that doctor-prescribed pharmaceuticals kill more than 100,000 Americans in hospitals each year.

The most implacable foes of holistic healing seem to believe that herbs can’t be trusted; their active compound must be synthesized and marketed as a prescription drug. This view implies that reliable medicinal wisdom was absent before randomized clinical trials began in the mid-20th century. These critics do not realize that humankind has been involved in a continuous, ongoing medical trial for the past 50,000 years. This colossal planetary experiment has been made up of countless single-case studies involving the use of herbs in every culture on earth. Every time an indigenous healer gave an herb to a sick individual, a new data point was added to the study, and the knowledge got around. If a Nobel Prize were given for arrogance, it would be awarded to the scoffers who breezily dismiss this accumulated wisdom.

Perhaps the only peer-reviewed medical journal to discuss t’ai chi and muscular dystrophy in the same issue, the bimonthly Alternative Therapies in Health and Medicine features reviews of current research, original findings in the field of complementary medicine, provocative essays, and interviews with innovative practitioners of the healing arts.

Larry Dossey, M.D., is the executive editor of Alternative Therapies in Health and Medicine, and the author of numerous books on holistic health and healing, including Reinventing Medicine. Excerpted from Alternative Therapies in Health and Medicine (May/June 2001). Subscriptions:$59/yr. (6 issues) from 101 Columbia, Aliso Viejo, CA 92656.