Millions of people take Gingko biloba because they think it keeps them smart. A recent study suggests they might be smarter to save their money ($107 million was spent on gingko in 2007 in the US alone).
Gingko has been touted for everything from altitude sickness to tinnitus, but the main claims have been for dementia, Alzheimer's disease, and improving memory. The evidence wasn't clear, so the National Center for Complementary and Alternative Medicine (NCCAM) funded a large trial to find out whether gingko could really delay the onset of dementia or Alzheimer's. They studied 3000 people over the age of 75 who were either normal or had mild cognitive impairment. It was a well-designed double blind placebo controlled trial lasting over 6 years. They found no difference in the incidence of dementia or Alzheimer's disease. Actually there were a few more cases of dementia and more hemorrhagic strokes in the gingko group than in the placebo group, but the difference wasn't statistically significant.
Even before this trial, the Natural Medicines Comprehensive Database (considered the "Bible" for herbal medicines and diet supplements) listed gingko only as "possibly" effective and "possibly" safe - it didn't even merit their "probably" safe or effective categories. They consider it "probably unsafe" in pregnancy.
There are other concerns. Gingko interacts with all sorts of other medications including Motrin. It can cause bleeding and should be discontinued 2 weeks before surgery. And there's no guarantee that you are getting what the label says. When ConsumerLab.com recently tested 7 gingko products, five failed the tests: two contained adulterated material, two contained less gingko than claimed on the label, and one was contaminated with lead.
This study didn't rule out the possibility that gingko might be found useful in other scenarios, but it falls into a pattern. The NCCAM has been spending hundreds of millions of taxpayer dollars to test commonly used diet supplements to find out what really works. They haven't found anything that works. They've found a lot of things that don't work. That would be useful if people would accept the results and stop using those supplements. Instead, they keep believing in the supplements and calling for more studies: let's try it on younger subjects, let's try a different dose, let's try it for another disease... You could keep dreaming up more studies forever.
To paraphrase the editorial that accompanied the study in the Journal of the American Medical Association: if you don't have clear evidence that it helps, and if you don't have clear evidence that it's harmless, it's probably not smart to take it.