Millions of Americans take the popular herbal supplement ginkgo biloba, hoping to preserve or improve their memory. According to a new study published in the Journal of the American Medical Association, ginkgo biloba does not appear to delay or prevent the onset of dementia in elderly adults.

Investigators from the University of Virginia School of Medicine and their colleagues conducted a clinical trial in 5 academic medical centers in the United States between 2000 and 2008 to determine the effectiveness of ginkgo biloba in reducing the incidence of Alzheimer disease and other dementias in elderly individuals. The trial involved 3,069 community volunteers aged 75 years or older who were treated with either twice-daily doses of ginkgo or a placebo. The volunteers were assessed every 6 months for dementia over an average follow-up period of 6 years. The investigators found that the rate of dementia among those who took ginkgo was not significantly different than among those who took placebo. In addition, they found that, among individuals who had mild cognitive impairment, ginkgo biloba had no effect on the rate of progression to dementia.

Americans spend nearly $250 million a year on ginkgo supplements. The results of this study suggest that ginkgo biloba does not prevent or delay dementia, a leading cause of age-related disability and long-term care placement in the United States.