What ginkgo is: A centuries-old Chinese herbal medicine, ginkgo comes from the dried leaves of the maidenhair tree (Ginkgo biloba). It contains a complex mix of compounds, but researchers have primarily focused on two particular chemical groups—flavonoids and terpenoids. Like aspirin, ginkgo can keep blood clots from forming and may increase blood flow. A standardized extract developed in Germany, EGb761, is the form used in many clinical trials and is widely prescribed there and in France for “cerebral insufficiency,” which can mean anything from confusion, memory impairment, anxiety and depression to headaches, tinnitus (ringing in the ears) and dementia. It’s also used for circulatory disorders, such as intermittent claudication (pain in the legs due to obstructed blood flow).
Claims, purported benefits: Improves blood flow and improves circulatory disorders, reduces blood clotting, has anti-inflammatory, antioxidant and neuroprotective effects. Effective against eye disease and tinnitus. Many people take ginkgo in hopes that it will sharpen their memory and concentration.
What the studies show
A dozen years ago, a study found that ginkgo improved mental functioning in people with Alzheimer’s, but despite a flood of studies since then, the evidence remains inconsistent. In one of the few studies to compare ginkgo with a standard drug approved for use in treating Alzheimer’s disease, a small Italian study in 2006 found ginkgo as effective as donepezil (Aricept) in improving memory and attention in people with mild to moderate Alzheimer’s. However, a review of 35 studies by the Cochrane Collaboration in 2007 concluded that the overall evidence for ginkgo as a treatment for dementia or cognitive impairment is “inconsistent and unconvincing.” In a 24-week German study published in the Journal of Psychiatric Research in 2012, the EGb761 extract was shown to improve cognition and behavioral problems better than a placebo in people with mild to moderate Alzheimer’s.
As for prevention trials, a large, well-designed study of healthy people 75 and older in 2008 found no evidence that ginkgo helps prevent dementia, including Alzheimer’s. In 2009, a follow-up study in the Journal of the American Medical Association found that the supplement did not slow cognitive decline or memory loss in any way. In 2012, a well-designed French study in Lancet Neurology looked at 2,850 people aged 70 and older with self-reported memory complaints, half of whom took the EGb761 extract twice daily, half a placebo. After five years, ginkgo did not slow the rate of progression to Alzheimer’s.
In 2013, a French observational study of people over 65 without dementia, published online in PLOS ONE, found that those who reported taking the EGb761 extract showed less decline in cognitive function during the long-term follow-up period than nonusers. This was not a randomized clinical trial, however, and there could have something else about the people taking the extract that accounted for reduced cognitive decline. For instance, they were better educated and less likely to use antidepressants, which can have an adverse effect on cognition.
A research review by the Cochrane Collaboration in 2013 concluded that the limited evidence about ginkgo as a treatment for tinnitus does not demonstrate that it is effective.
Also in 2013, a government study unearthed evidence that ginkgo extract causes cancer in rodents. This doesn't necessarily translate to people, of course, but these kinds of toxicity studies are an important part of assessing cancer risk.
Side effects: Rare side effects include headache, stomach upset, palpitations, dizziness and rashes. Because some cases of ginkgo-related bleeding have been reported, it should be avoided before surgery and used cautiously with aspirin, warfarin (Coumadin), or other drugs that affect blood clotting. It may increase the sedative effects of certain antidepressants or increase blood concentrations of some drugs used for treating hypertension. Its safety during pregnancy and breastfeeding is unknown.
Bottom line: Though ginkgo is one of the best-studied herbs, there is no convincing evidence it has any effect on memory or other mental functions in healthy older people—or that it has any health benefits, period. Add that to the new safety questions, and you would be wise to steer clear of supplements containing the herb. Still, if you or a family member has Alzheimer’s or another dementia, you might talk to your doctor about trying ginkgo, but keep in mind that drug treatments may be better. Furthermore, commercially available products may be different from the preparations used in clinical studies, so you may not get the same effects. Some ginkgo supplements sold in the United States claim to be the standardized extract used in research, but you can’t be sure.