Dr. Steven Dekosky responds:

There are theoretical reasons to suspect that Ginkgo biloba might be helpful in preventing—or at least slowing—the development of Alzheimer's disease through the supplement's powerful antioxidant effects. In addition, some animal and cell culture models have suggested that Ginkgo biloba might have some specific effects on one of the proteins, Beta-amyloid, involved in the disease.

But we won't know if it is effective in preventing dementia until we have the results of an ongoing 3,000-person clinical trial. That trial, which is sponsored by the National Center for Complementary and Alternative Medicine and the National Institute on Aging at the National Institutes of Health, will be completed in 2008.

Several studies have assessed Gingko biloba in dementia or Alzheimer's disease and found variable effects. The most recent large placebo-controlled double-blind study, which tested the supplement for six months in people who had already developed Alzheimer's disease, found that Ginkgo biloba did not have significant effects compared to placebo. A secondary analysis of data from that trial seemed to show that the supplement might improve behavioral symptoms of Alzheimer's, but since the study wasn't originally designed to look at this, more studies would be needed to look at that specific outcome.

Even though there's no proof that Ginkgo biloba works, many people take it in hopes that it will be helpful.

What we do know is that it probably isn't harmful. It doesn't appear to have interactions with any of the currently prescribed Alzheimer's medications and there don't appear to be any serious side effects.