You Use That Stuff, Too?

Some athletes take ginseng to improve stamina, but here, too, the evidence is mixed. Several studies suggest ginseng may lower blood sugar in people with type 2 diabetes, but long-term effects and proper dosage haven't been studied.

"Well-conducted trials do not support the efficacy of ginseng to treat any condition," wrote Edzard Enrst, a British researcher, in a 2002 review article in the Annals of Internal Medicine.

While serious side effects are rare, some people taking ginseng have reported diarrhea, sore throat, excitability, anxiety, depression or insomnia. Because ginseng may have some estrogen-like effects, the Mayo Clinic recommends that people with hormone-sensitive conditions -- such as breast or uterine cancer -- avoid ginseng. Some case reports suggest ginseng may thin the blood, making it potentially dangerous for people on blood-thinning medications like warfarin.

Ginkgo Biloba

Imagine if a natural product could prevent Alzheimer's disease and dementia or even improve concentration and memory. Extracts from the leaves of the ginkgo biloba tree, imported to the United States from China in 1784, can do all that, some say, plus relieve a multitude of other ills, including altitude sickness, premenstrual syndrome, impotence, depression and glaucoma.

All this may explain why ginkgo is one of the top-selling herbs in the United States, accounting for some $130 million in sales in 2003, according to the Nutrition Business Journal. Ginkgo was the third most popular natural product in the NCCAM survey; 21 percent of those who took herbal supplements reported taking it.

But does it work? "Ginkgo extract has a number of chemical activities that theoretically keep dementia away, but you've got to do the study to see," said Steven DeKosky, chairman of the department of neurology at the University of Pittsburgh School of Medicine. A 1997 study in JAMA found ginkgo could improve cognitive performance in people with dementia. But a rigorous 2004 review by a the Cochrane Collaboration, a U.K.-based nonprofit group that analyzes data from clinical trials, recommended further study, despite what it called "promising evidence" of benefit.

With the help of NCCAM funding, DeKosky is conducting the largest ginkgo trial ever, which will follow 3,000 people with normal mental function or mild cognitive impairment over at least five years. In addition to tracking how many subjects develop dementia, researchers hope to learn whether ginkgo could decrease heart attacks, strokes and related deaths.

Because ginkgo may change insulin and blood sugar levels, people with diabetes or hypoglycemia should consult a doctor before using it. Some studies suggest ginkgo may increase bleeding, making it dangerous for people with bleeding disorders or on blood-thinning drugs. Ginkgo seeds are poisonous and can cause seizures.

Garlic Supplements

Promoters say garlic can lower cholesterol and blood pressure, prevent hardening of the arteries and protect against cancer. Skeptics say it's as likely to keep away vampires.

The Agency for Healthcare Research and Quality, a federal agency that develops evidence-based reports on medical treatments, conducted a systematic review of the evidence and found that while garlic supplements may temporarily lower LDL ("bad" cholesterol), it doesn't appear to to raise HDL ("good" cholesterol) or confer long-term protection against heart disease. The agency found no proof that it lowered blood pressure or treated diabetes and called the evidence on cancer prevention inconclusive.

Other than smelly breath and body odor, possible adverse effects associated with garlic include abdominal pain, asthma and intestinal obstruction. A few studies suggest garlic may cause bleeding or blood-thinning, so garlic supplements are not recommended for people who are on blood-thinning medication. Severe allergic reactions are also possible.