Although often billed as a memory and cognition enhancing product, the medicinal herb Ginkgo biloba does not stave off cognitive decline or help prevent dementia and Alzheimer's disease, according to a report in the Journal of the American Medical Association this week.

In the Ginkgo Evaluation of Memory (GEM) Study, use of the herbal product was actually tied to higher risks of dementia and Alzheimer's disease, but the associations did not reach statistical significance.

"Ginkgo biloba is widely used for its potential effects on memory and cognition," Dr. Steven T. DeKosky, from the University of Virginia School of Medicine, Charlottesville, and colleagues note. However, "to date, adequately powered clinical trials testing the effect of Ginkgo biloba on dementia incidence are lacking."

In the GEM study, 2,587 older adults (75 years of age and older) with normal cognition and 482 with mild cognitive impairment were allocated to receive a twice-daily dose of Gingko biloba extract (120 milligrams) or placebo.

The researchers found no statistical difference in rates of dementia or Alzheimer's disease between the two groups. Overall, 277 subjects taking Ginkgo and 246 subjects taking placebo developed dementia over the course of the study, which lasted a median of about 6 years.

Compared with placebo, Ginkgo use was associated with a slightly increased risk of dementia and Alzheimer's disease.

There was also no evidence that Ginkgo use reduced progression to dementia in subjects with mild cognitive impairment.

This study, wrote Dr. Lon S. Schneider in an editorial in the journal, "adds to the substantial body of evidence that Gingko biloba extract as it is generally used does not prevent dementia in individuals with or without cognitive impairment and is not effective for Alzheimer's disease."

"Users of this extract should not expect it to be helpful," continued Schneider, who is with the University of Southern California, Los Angeles.

Moreover, the potential adverse effects of Gingko biloba extract, Schneider points out, including stroke or "mini-strokes," illustrate why it is "untenable to recommend a drug or nutriceutical in the absence of efficacy evidence simply because it could possibly help and initially appears harmless."