Elderberry extract and acai to boost the immune system. Black cohosh to lessen the discomforts of menopause. Soy capsules to prevent bone loss and prostate cancer.

Many botanical supplements—made from the seeds, bark, leaves, flowers and stems of a wide range of plants—have been widely used as folk remedies for centuries. Americans have been consuming growing quantities of the supplements in hopes of warding off disease and easing symptoms of various conditions. But there is scant scientific evidence to support their health benefits.

Now, the federal government is stepping up research into the safety and effectiveness of a wide range of over-the-counter supplements, including plant oils, garlic, soy, elderberry, licorice, black cohosh, St. John's wort and the Asian herb dong quai. The aim is to better understand how compounds in the plants affect health and to help consumers make more informed choices about supplements, which can interact with prescription drugs, cause side effects or lead to new health risks. Sales of botanical supplements in the U.S. topped $5 billion last year, up 17% from five years earlier, according to the non-profit American Botanical Council.

"Sometimes people assume because a product is natural, it is also safer. But these compounds can have both benefits and potential side effects and we need to understand both of those," says Floyd Chilton III, director of the Center for Botanical Lipids and Inflammatory Disease Prevention at Wake Forest University Baptist Medical Center in Winston-Salem, N.C. Dr. Chilton's center received a $7.5 million federal grant to study botanicals, including whether plant oils such as echium and borage can help play a role in preventing cardiovascular disease, asthma and diabetes.

"People are using supplements for purposes for which they were not intended," such as treating health conditions they have self-diagnosed, or using multiple supplements in combination with prescription medications, says Marguerite Klein, director of the Botanical Centers Research program at the National Institutes of Health. One concern, she says is the heavy use by women of black cohosh to treat menopause symptoms, such as hot flashes. Limited research seems to support the black cohosh's benefit. But it isn't known how the botanical works. Black cohosh has been linked in some patients to liver damage, and breast-cancer patients are often advised to avoid using it because its effects on breast tissue are unknown.