The authors of the GEM study note that it's possible potential benefits from ginkgo biloba supplementation may take many more years to manifest. That's because the neurological changes associated with dementia take place over a long period of time. And indeed, all of the studies we looked at used older subjects. But in an editorial accompanying the GEM study, Lon S. Schneider, M.D, of the Keck School of Medicine at the University of Southern California, concludes, "Users of this extract should not expect it to be helpful."

It seems that counting on ginkgo biloba for any cognitive benefits might amount to a leap of faith, and one that is not without cost. Americans spent about $107 million on ginkgo biloba supplements in 2007, according to the Nutrition Business Journal. And a year's supply can cost about $200 per person. But until there is more convincing evidence of efficacy, you may be better off saving that money instead.

And, while ginkgo is widely considered safe, there is some concern about increased risk of bruising and bleeding, and potential drug interactions. If you're considering taking a natural medicine, it's always a good idea to talk it over with your doctor first.

—Kevin McCarthy, associate editor

For more, see our Natural Medicine Ratings and drug interactions for ginkgo biloba (subscribers only), and our Treatment Ratings for Alzheimer's disease and dementia (subscribers only). For those who have Alzheimer's disease, or have a loved one who does, see our free Best Buy Drug Report for treatment comparisons.