The leaf of the maidenhair tree, Ginkgo biloba, has been used as herbal medicine in China since the fifteenth century. The leaves were traditionally used for benefiting the brain and for treatment of lung disorders. In modern times, Ginkgo biloba is a popular supplement that is widely used for its potential effects on memory and cognition. A standardized extract is widely prescribed for the treatment of a range of conditions including memory and concentration problems, confusion, depression, anxiety, dizziness, tinnitus and headache.
The mechanism of action of Ginkgo is supposed to be due to components that increase blood supply by dilating blood vessels, reducing blood viscosity, and reducing free radicals, but recent studies show that the purported benefits of ginkgo for the brain are exaggerated and cannot be demonstrated scientifically. One study concludes that Ginkgo biloba appears to be safe in use with no excess side effects compared with placebo, but the evidence that Ginkgo has predictable and clinically significant benefit for people with dementia or cognitive impairment is inconsistent and unconvincing. A second study shows that Ginkgo biloba taken at a dose of 120 mg twice a day was not effective in reducing either the overall incidence rate of dementia or Alzheimer disease incidence in elderly individuals with normal cognition or those with mild cognitive impairment.
The good news is that Ginkgo is not harmful. The bad news is that many people have been wasting their money on an ineffective supplement.
The leaves of Ginkgo biloba trees turn bright yellow in the autumn. The trees are popular ornamental trees which are survivors from the days of the dinosaurs.
 Birks J, Grimley Evans J., Ginkgo biloba for cognitive impairment and dementia. Cochrane Database Syst Rev. 2007 Apr 18;(2):CD003120.
 DeKosky ST, Williamson JD, Fitzpatrick AL, et al., Ginkgo biloba for prevention of dementia: a randomized controlled trial, JAMA. 2008 Nov 19;300(19):2253-62.