The Ginkgo biloba for the Evaluation of Memory (GEM) Study involved 3,069 participants age 75 or older, who had either normal cognition or mild cognitive impairment.
The study aimed to evaluate ginkgo for its effects on overall cognitive decline, functional disability, incidence of cardiovascular disease and stroke, and total mortality.
The participants were randomised to receive twice-daily doses of either 120 mg of ginkgo extract or placebo.
The dose of ginkgo was selected based on prior clinical study results that found 120 mg twice daily to be the most effective dose.
The study showed that 240 mg of ginkgo daily has no effect on the onset of dementia or development of Alzheimer's.
"The results were disappointing and surprising," said Gregory Burke, M.D., M.Sc., the lead investigator for the Wake Forest University Baptist Medical Center clinical site and Jeff Williamson, M.D., M.H.S., principal investigator for the GEM Study Clinical Coordinating Center at Wake Forest Baptist.''
"It is very unlikely that ginkgo biloba is effective at any dose over a five-year period and in anyone over 75 years old," Williamson said.
"It is also ineffective in people with signs of early memory loss. What is not known yet is whether the effect of ginkgo biloba might require taking the drug for many, many years, say 15 years, before there is even a sign of memory loss," he added.