Use of the herb Ginkgo biloba, claimed to have beneficial effects on memory and cognition, was not effective in reducing the rate of dementia or Alzheimer's disease among more than 1,500 elderly study participants after several years of use, according to a study in the November 19 issue of JAMA.

Ginkgo biloba is prescribed in some areas of the world for preservation of memory; however, there are no medications approved for prevention of dementia, and to date, no clinical trial of adequate design and size has evaluated the safety and effectiveness of Ginkgo biloba in the primary prevention of dementia.

Steven T. DeKosky, M.D., of the University of Pittsburgh, Pa., at the time of the study, and the Ginkgo Evaluation of Memory (GEM) Study Investigators, assessed the effectiveness of Ginkgo biloba in dementia prevention. The study was a randomized, placebo-controlled clinical trial conducted at five academic medical centers in the United States between 2000 and 2008 with a median follow-up of 6.1 years. The trial included 3,069 community volunteers age 75 years or older with normal cognition (n = 2,587) or mild cognitive impairment (MCI; n = 482) at study entry, who were assessed every 6 months for dementia. Participants were randomized to receive either a twice-daily dose of 120-mg extract of Ginkgo biloba (n = 1,545) or placebo (n = 1,524).

The researchers found that during the intervention period, 523 participants were diagnosed with dementia, 246 (16.1 percent) in the placebo group and 277 (17.9 percent) in the Ginkgo biloba group. Of the total dementia cases, 92 percent were classified as possible or probable AD, or AD with evidence of vascular disease of the brain. The rate of total dementia did not differ between participants assigned to Ginkgo biloba vs. placebo (3.3 dementia cases/100 persons, per year exposed, among persons randomized to Ginkgo biloba vs. 2.9/100 persons, per year exposed, among persons randomized to placebo). The rate of Alzheimer-type dementia also did not differ between the two treatment groups (3.0/100 persons, per year exposed vs. 2.6/100 persons, per year exposed). Ginkgo biloba also had no effect on the rate of progression to dementia in participants with MCI.

The adverse event profiles for Ginkgo biloba and placebo were similar and there were no statistically significant differences in the rate of serious adverse events.

"Based on the results of this trial, Ginkgo biloba cannot be recommended for the purpose of preventing dementia," the authors write.

"These results confirm that randomized trials remain critical to the spectrum of translational research necessary to develop new therapies and to determine whether the purported in-vitro, epidemiologic, and surrogate measures of therapeutic benefit are true not only for traditional pharmaceutical therapies but also for complementary therapies. Of almost equal importance from these results is the provision of a strong rationale for including older individuals in randomized trials testing promising interventions for preventing or delaying dementia onset."
In an accompanying editorial, Lon S. Schneider, M.D., of the University of Southern California, Los Angeles, comments on the findings of DeKosky and colleagues.

"Despite 2 decades of research with standardized extracts of Ginkgo biloba, considerable uncertainty about its pharmacology and clinical effects remains. Preclinical scientific reports exude promise but generally have not identified the relevant active molecules of this biochemically complex extract, and the preclinical promise has not translated to clinical research benefits. The clinical research, in turn, has not adequately defined potential cognitive indications, potentially effective dosing ranges, pharmacodynamic markers, or convincing evidence for efficacy for any one cognitive condition. The GEM study adds to the substantial body of evidence that Ginkgo biloba extract as it is generally used does not prevent dementia in individuals with or without cognitive impairment and is not effective for Alzheimer disease."