Ginkgo biloba, an herb said to improve memory and concentration, provides no benefits for healthy adults, according to a report in the Journal of the American Medical Association.

Dr. Paul Solomon of the Memory Clinic in Bennington, VT, and researchers at Williams College in Massachusetts enrolled 230 healthy adults over the age of 60 in the double-blind study.

"The results indicate that when taken following the manufacturer's instructions, ginkgo provides no measurable benefit in memory, attention, or concentration in healthy older adults," Solomon said.

Gingko, an antioxidant used for centuries in Chinese medicine, has been widely promoted as useful in treating Alzheimer's disease and is approved for that purpose in Germany.

Dr. Steven DeKosky, chairman of the University of Pittsburgh's neurology department, said Solomon's study doesn't address whether larger doses taken for a longer duration or taken by people who already have memory problems would be beneficial.

DeKosky is the lead researcher in a government-funded study examining whether ginkgo in doses equal or double those in Solomon's study can help prevent Alzheimer's .

Participants in his study are older than 75, have normal mental function or slight memory problems and are taking ginkgo for five years.

Other sources: Journal of the American Medical Association