Ginkgo biloba fails drug test; herb fares no better than placebo against dementia.

The supplement ginkgo biloba has failed to ward off Alzheimer's disease or other forms of dementia any better than a placebo in a long-term trial, researchers report in the Nov. 19 Journal of the American Medical Association.

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"This is tremendously disappointing," says study coauthor Steven DeKosky, a neurologist at the University of Virginia School of Medicine in Charlottesville.

In earlier lab tests, ginkgo extract showed an ability to protect brain cells from the sort of problems that occur in Alzheimer's patients. In animal tests, the herb inhibited amyloid-beta clumping, widely assumed to play a role in Alzheimer's.

But the new, eight-year study, the largest clinical trial ever specifically designed to test a drug or supplement for Alzheimer's prevention, casts serious doubt on ginkgo's usefulness. European researchers are now conducting a similar trial, DeKosky says. If those findings are also negative, he says, "that would clinch it."

Starting in 2000, DeKosky, then at the University of Pittsburgh, and his colleagues randomly assigned more than 3,000 people, average age 79, to receive two ginkgo pills a day or placebo pills. All participants were free of Alzheimer's disease or other dementia at the start, but some in each group began with some mild cognitive impairment. The researchers tracked the volunteers' progress until 2008.

After an average of six years, roughly equal numbers of people taking ginkgo and people taking placebos had developed dementia, which in the vast majority of cases was Alzheimer's disease.

The study "adds to the substantial body of evidence that G. biloba extract as it is generally used does not prevent dementia," writes Lon Schneider of the University of Southern California in Los Angeles in the same issue of JAMA.