According to a clinical trial reported Tuesday, the elixir of eternal mental acuity, the herbal extract ginkgo biloba in fact does not prevent or delay the progression of dementia or Alzheimer's disease. The findings were published in the November 19 issue of the “Journal of the American Medical Association.”

"We found that giving a standardized dose of ginkgo biloba over a period of time does not slow down the incidence rate of dementia or Alzheimer's disease," said the study's lead author, Dr. Steven DeKosky, who was chair of the department of neurology at the University of Pittsburgh School of Medicine and Medical Center at the time of the study.

The results suggest that the $250 million that Americans spend on ginkgo every year may largely be a waste of money. The study followed 3,069 adults age 75 and older (about half of them with normal cognitive function and half with mild cognitive impairment) for an average of nearly six years. One group received a twice-daily dose of ginkgo while the other received a placebo.

DeKosky says that there were two important conclusions to take away from the study: Ginkgo biloba is ineffective in battling dementia, but also that the herb is relatively safe. Still, some research has suggested that it may cause excessive bleeding. During the study period, 523 cases of dementia were diagnosed. Of those, 246, or 16.1 percent, were in placebo users, and 277, or 17.9 percent, were in people taking ginkgo biloba.

Dr. Murali Doraiswamy of Duke University Medical Center in Durham, North Carolina, noted that the findings will lead him to actively discourage people from taking ginkgo with the aim of preventing Alzheimer's. The disease is incurable and it affects more than 5.2 million Americans. Alzheimer's passed diabetes two years ago as the sixth-leading cause of death in the U.S., according to the Centers for Disease Control and Prevention.