But Stepp argues that the backyards of indigenous peoples are more likely sources. He said that if a pharmaceutical researcher gave indigenous villagers a list of a hundred illnesses and asked them to find plant remedies for each, "they'd spend most of the time right down the trail."
The weeds and other plants that grow near indigenous villages are the most well known and widely used, Stepp said. "Are there likely [medicinal] plants deep in the jungle? Yeah, there's a good chance of it. But it's also likely that no one else [including indigenous peoples] knows about it," he said.
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The properties that make a weed a weed, and thus able to thrive in disturbed habitats, are what make the plants potentially beneficial.
Weeds are full of bioactive compounds. These are chemicals that weeds have evolved over thousands of years to compete against other plants and to prevent predators, such as insects, from munching their leaves.
These compounds "are toxic to predators. But [when] used in the right dose, they have therapeutic benefits for humans," Stepp said.
Coley, the University of Utah biologist, said competition between plants and insects have also forced slow-growing, nonweedy tropical plants to evolve chemical defenses.
Meanwhile Stepp said his 2004 study results suggest that, in addition to exploring the rain forest for medicinal plants, it makes sense to look at the 8,000 or so weeds that grow closer to home.
The anthropologist doesn't think drug companies share that view. "The difference between wanting to find new medicines and wanting to find new medicines to make a profit is a very wide gulf," he said.
Stepp said that to profit from a plant-derived drug, pharmaceutical companies need to patent new compounds. But the chemistry of most weeds is already described and in the public domain, he noted.
Regardless of whether new drugs are developed from weeds, Stepp said weed research could lead governments to respect and promote traditional medicinal practices, especially in parts of the world with limited access to modern health care facilities.
"In Western, industrialized countries, healing is very much a specific act. You are taught to not self-medicate. If you're sick, you go to a doctor, and they'll tell you what's wrong," he said. "That's not true for the vast majority of the world. They do treat themselves."
Stepp and his colleagues published their study in the June 2004 issue of the Journal of Ethno-Pharmacology.
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