Findings from a large, long-term study dispel the notion that ginkgo biloba—a popular herbal supplement widely purported to improve memory and cognition—prevents dementia or Alzheimer’s disease (JAMA. 2008;300:2253-2262).

According to the NIH, cosponsor of the trial, the Ginkgo Evaluation of Memory (GEM) study was the largest clinical trial thus far to evaluate ginkgo’s effect on the occurrence of dementia. Conducted over the course of eight years at four sites, GEM enrolled 3,069 participants aged 75 years or older with normal cognition or mild cognitive impairment (MCI). Subjects, who underwent medical and neuropsychologic screening, were randomly assigned to receive twice-daily doses of either 120 mg of ginkgo extract or a placebo.

Followed for an average of approximately six years, 277 members of the ginkgo group (17.9%) were diagnosed with dementia, compared with 246 (16.1%) in the placebo group. “In this study, ginkgo biloba at 120 mg twice a day was not effective in reducing either the overall incidence rate of dementia or Alzheimer’s disease in elderly individuals with normal cognition or those with MCI,” notes lead author Steven T. DeKosky, MD, vice president and dean of the University of  Virginia School of Medicine in Charlottesville.

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On the positive side, use of ginkgo biloba did not appear to cause bleeding or other significant adverse effects.