Ginkgo biloba: A Cognitive Enhancer?

Summary— Ginkgo biloba is an herb often used as an alternative treatment to improve cognitive functions. Like most herbal treatments, the use of ginkgo is poorly regulated by government agencies, on the basis of either its efficacy or its health risks. This article reviews the experimental evidence available regarding efficacy, neurobiological actions, and health risks. Findings obtained in studies of humans often include demonstrations of rather mild cognitive enhancement. Interpretation of these findings is complicated by somewhat inconsistent findings, by experimental designs that do not permit identification of cognitive functions susceptible to the influence of ginkgo, and by the paucity of direct comparisons with other treatments. The number of peer-reviewed reports of studies in nonhuman animals is surprisingly small. In this small set, the findings reveal mild behavioral effects that might be attributable to actions on cognitive functions. However, these experiments in rodents, like those in humans, do not involve the use of designs to assess ginkgo’s effects on particular cognitive attributes, and generally do not include direct comparisons with other treatments. Interpretation of the findings is further complicated by evidence, obtained in studies of both humans and rats, showing that a single administration of the treatment enhances performance on cognitive measures. If ginkgo has effects on cognition, there should be effects evident on biological processes as well. Neurobiological studies have largely examined the effects of chronic ginkgo administration, mirroring the most common design in behavioral studies. However, the addition of findings that single administration of ginkgo may influence behavior directs biological investigations to short-term actions of the treatment. Biological effects of ginkgo include vasodilation, protection of neurons from oxidative stress, and actions mediated by effects via neurotransmitters. Adverse reactions to ginkgo consumption have been observed but are relatively rare. Collectively, the behavioral literature reviewed cannot be used conclusively to document or to refute the efficacy of ginkgo in improving cognitive functions. At best, the effects seem quite modest. In particular, it is questionable whether effects of ginkgo, if present, are equal to those obtained by administration of acetylcholinesterase inhibitors, hearing an arousing story, or ingesting glucose. Much as there seems today to be a gene for every disease, and for every psychological construct, there appears to be an herb for every ailment. The use of dietary supplements and natural products to improve psychological functions is widespread throughout the world. In most cases, the use of dietary supplements to treat psychological disorders, or to augment normal functions, is based far more on folklore than on experimental findings. In the United States, it is easy to use such treatments because the federal government regulates them relatively weakly, compared with pharmaceuticals. Advertisement and labeling claims are monitored, but there remain many sources that promote using herbal treatments for a wide range of maladies. The widespread consumer use of dietary supplements to address psychological and other concerns warrants more attention to the efficacy of these treatments and to their possible health risks. Even if they do not cause medical problems, they have real costs—money, time, and avoiding other sources of treatment. It is in this context that the present report examines the experimental bases for the use of ginkgo as a treatment to improve cognitive functions. The use of ginkgo for biological and psychological purposes, including to improve alertness, can be traced back for centuries in traditional Chinese medicine. Today, ginkgo is perhaps the most widely used herbal treatment selected specifically to augment cognitive functions. The use of ginkgo as a cognitive enhancer is especially prevalent in Europe. In recent years, ginkgo leaf extracts have been given the approval of the German Bundesgesundheit Association for treating dementia. In the United States, the National Institute on Aging is currently supporting a clinical trial to evaluate the efficacy of ginkgo in treating the symptoms of Alzheimer’s disease. Although the findings of the clinical trials will likely provide the best data from which to determine whether ginkgo affects cognitive decline in dementia, the purpose of the present report is to evaluate the evidence for and against the usefulness of