Study: Weeds Make the Best Medicine

Researchers who are scouring the tropical forests for exotic plants that can heal the sick may be overlooking the obvious.

Look not in the forest, advises anthropologist John Richard Stepp of the University of Florida. Look, instead, at your feet and savor the medicinal values of ordinary weeds.

That's right. Weeds.

Those miserable plants that always turn up where they are least welcome account for more than a third of the plants used in pharmaceuticals, according to Stepp's research. That's despite the fact that only about 3 percent of the world's plant species are classified as weeds.

"There has been this sort of promotion of tropical forests as the place to find drugs, and I started to wonder if that jived with what had already been discovered," Stepp says. After combing through the technical literature Stepp concluded that weeds have been a veritable gold mine for pharmaceutical companies in the past, and in many cases far more beneficial than more exotic plants found deep in the forest.

Stepp published his findings in the current issue of the Journal of Ethno-Pharmacology.

Local Remedies Tap Weeds

He figures the poppy, used to produce morphine, is the best known medicinal weed, but there are many others. Weed extracts are used for the motion sickness drug scopolamine, as well as the cancer medicines vinblastine, for Hodgkin's disease, and vincristin, for childhood leukemia, he says.

Some gardeners may not view the poppy as a weed, but it fits the classic definition.

"Basically, weeds are plants that are aggressive, fast growing, and thrive in disturbed areas," Stepp says.

My dictionary calls a weed "any undesired, uncultivated plant that grows in profusion so as to crowd out a desired crop."

That's a stuffy phrasing of the old gardener's definition of a weed. It's anything that grows where you don't want it to grow. By any definition, weeds are all around us, and they arrive in great numbers soon after the spade is plunged into the soil.

"If you clear an area out, the plants you are going to see in a couple of weeks are weeds," Stepp says.

Stepp's campaign in defense of the lowly weed began more than a decade ago when he was studying the Mayans in the highlands of the Mexican state of Chiapas. The water was contaminated with parasites, and it didn't take long for Stepp to come down with a stomach ache.

He asked the local people how they coped with the problem and they gave him a plant they called the "broom tree," which they boiled and drank. Stepp tried it, he says, and it worked.

The broom tree, Baccharis vaccionoides, is a weed that grows in disturbed areas on the outskirts of the forest.

Stepp found that the Mayans used weeds for all sorts of illnesses, including colds, skin rashes, and ordinary aches and pains. The people he has studied for more than a decade have no choice but to brew their own medicines. They live high in the mountains, far from health care facilities, and plants are their primary line of defense against illnesses of all sorts.

That's why, he says, children there can name at least 100 different plants. They know their value.

"The highland Mayan have more than 1,500 medicinal plants," Stepp says.

And most of the plants they use are found in cleared areas, outside the hot, steamy jungle. They are just common weeds.

Tough Roots Make Good Meds

Stepp remembered that years later when he was working as an instructor at the University of Georgia. As a research project, he had his students collect plants alongside a railroad track, and in a dense forest. They identified all the plants, and checked to see which ones were used historically by Native Americans.

"We found very few in the forest," Stepp says. "But we found a huge number alongside the railroad track."

Like the Mayans, those early Americans found weeds to be the most helpful in treating their maladies.

It all makes sense, Stepp says, when you consider the plight of the weed. Easy prey for foraging animals and insects, weeds thrive because they came up with ways of protecting themselves.

"Weeds developed defense compounds that protect them from animals and insects," Stepp says.

Generally, those compounds make weeds taste bitter. That's one of the ways that early Mayans figured out which plants might have medicinal value.

"Taste is a big marker," Stepp says. "That's usually an indication that they might have some medicinal value. Probably the most important class of compounds for medicinals are alkaloids and alkaloids generally tend to be bitter. So just by tasting it, you can figure out that this plant has alkaloids in it, and alkaloids often are useful medicinally."

Of course, that procedure probably had disastrous results for some early experimenters. Some plants are very toxic if eaten, like brugmansia, or "angel's trumpet," which is mashed into a paste and used by the Mayan to reduce swelling. It works if applied externally, Stepp says, but it's poisonous when eaten.

So Stepp doesn't recommend that we venture forth and eat weeds. But he does suggest that researchers pay a little more respect to plants that are cursed and despised by gardeners around the world.

Even the voracious dandelion suffers from an unfair rap, he says. The Mayans use it to treat colds, and Native Americans boiled it into tea.

Lee Dye’s column appears weekly on A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.