Elderly people who took Ginkgo biloba every day for six years had as many difficulties with recall as those who took a fake supplement, the largest study of its kind has shown.
At least 100,000 people in Britain are thought to regularly take the supplement, which has been widely credited with improving memory and concentration.
Made from the leaves of the Ginkgo tree, the Chinese herbal remedy has been used as a traditional medicine for centuries.
It is thought to contain chemicals which help the flow of blood around the body, which advocates believe will help protect the brain against decline.
But the researchers who carried out the latest study warned that the supplement appeared to have no effect on warding off age-related memory problems.
Beth Snitz, from the University of Pittsburgh, who led the study, said: “Ginkgo biloba is marketed widely and used with the hope of improving, preventing, or delaying cognitive impairment associated with ageing and neurodegenerative disorders such as Alzheimer's disease.
“We (found) no evidence that Ginkgo biloba slows the rate of cognitive decline in older adults.”
For the study the team followed 3,069 volunteers, all of whom were aged between 72 and 96 years old and were given either a dose of the herbal supplement or a placebo twice a day for more than six years.
The findings are published in the Journal of the American Medical Association (JAMA).
Earlier studies have suggested that Ginkgo biloba could have other health benefits apart from memory, including reducing damage to the brain during a stroke.