"If I had one place to go to find medicinal plants, it wouldn't be the forest," said John Richard Stepp, a UF anthropologist who did the study. "There are probably hundreds of weeds growing right outside people's doors they could use."
Stepp combed through scientific journals and studies to determine which drugs on pharmacy shelves come from plants as opposed to those synthesized in a laboratory.
In a classic case of looking afar rather than at your feet, he found that although only about 3 percent of the world's quarter-million plant species are weeds, they make up more than a third – 36 – of the 101 plant species used in pharmaceuticals. In drug companies' quests to discover new remedies, weeds – short-lived, herbaceous, fast-growing plants that thrive in areas of human disturbance – that sprout along the outskirts of jungles and may have healing properties are routinely overlooked for flora ballyhooed for their disease-fighting qualities that are growing deep within woods, he said.
Perhaps the world's best-known medicinal weed is the poppy, from which morphine is derived, Stepp said. Scopolamine, an important drug for treating motion sickness, also is weed-based, as are the cancer medicines vinblastine, for Hodgkin's disease, and vincristin, for childhood leukemia, he said.
"With all the emphasis on the tropical rain forests, an entire area is being missed in natural products research," said Stepp, whose results appear in the current issue of the Journal of Ethno-Pharmacology. "These findings suggest that we need to broaden our horizons if we're going to search for new drugs from plants."
The plant-derived pharmaceuticals Stepp studied are single compounds extracted from a plant and used in a pharmaceutical, and are different from herbal medicines, such as ginkgo biloba and garlic, that have gained increasing popularity in recent years, he said.
Stepp said he got the idea for his study while working in the highlands region of the southwestern Mexican state of Chiapas. He found the area's Mayan residents use weeds for all sorts of day-to-day illnesses, such as common colds, upset stomachs, skin rashes, and aches and sprains.
For the vast majority of the 800,000 Mayans living in this area – where the elevation ranges from 1,500 to 8,000 feet, and steamy jungles give way to cloud-shrouded mountains – medicinal plants are the primary source of health care, Stepp said.
"They don't go to the doctor when they're sick because they don't have a doctor," he said. "They treat themselves, and they treat themselves very effectively with the plants that are around. What people don't realize is that two-thirds of the world's population relies on plants in this way."
Because of parasites in the water supply, an upset stomach is a common health problem for the Mayans, who often treat it by boiling the weed baccharis vaccionoides, which they call "broom tree," Stepp said. Various weeds to treat cold and respiratory problems also are self-prescribed because despite the tropical weather, the mountainous area gets cold at night and experiences frequent rain.
While some weed compounds are crushed up into a tea-like substance to drink, other plants, like brugmansia or "angel's trumpet," are mashed up into a paste used topically to reduce swelling, aches and pains, Stepp said. "Angel's trumpet has become somewhat notorious in the United States because there have been some cases of poisonings from people ingesting it, but it works pretty effectively when applied externally to the skin," he said.
Stepp said he was struck by how the Mayans were "natural botanists" who made plants a central part of their lives. "We worked with 4- and 5-year-old kids who could name 100 plants," he said. "An American kid might be able to name 100 Pokemon characters, but if you ask him the names of three plants, he would probably have a real hard time."
Americans may be able to get similar benefits from weeds as do people in developing countries, although he warns that people shouldn't experiment on their own.
In a classroom experiment with 15 undergraduate students in Georgia, Stepp had about half collect plants from weedy fields and half pick them from a forest. Using a database of major plants developed by Daniel Moerman, an anthropologist at the University of Michigan at Dearborn, to identify the specimens, the students found that as many as 50 plants plucked from the fields had been used medicinally by Native Americans compared with only 12 of those they gathered from the forest, he said.
"The realization that medicinal plants are readily available in a living pharmacy right outside the door and along the sides of trails rather than deep in the forest could lead governments to encourage and promote traditional medicinal practices," Stepp said. "They are readily available, cost nothing to gather and are often more effective."
Moerman, author of the book "Native American Ethnobotany," said he agreed that plants at hand are desirable for treating common illnesses. "There are good reasons why weeds – adventive species growing in disturbed soil – should be particularly useful as medicines," he said. "And one of the things human beings – especially after the invention of agriculture – are good at is disturbing soil. So it all works out well to have right at hand the plants you need for treating common illnesses."