Keris Krennhrubec, Diana Zuckerman, PhD, Katherine Ip, and Caitlin Kennedy, PhD, National Center for Health Research
Ginkgo biloba has been used in traditional Chinese medicine for thousands of years, and today it is one of the most popular herbal supplements, widely advertised as an antioxidant that helps prevent memory loss and dementia. Like most herbal products, however, there have been few clinical studies to see if these claims are accurate. Thanks to lobbying by companies, dietary supplements do not have to be evaluated and approved by the Food and Drug Administration (FDA) to ensure that they are safe or effective. However, studies by independent researchers suggest that these supplements may be very dangerous.
A 2008 study by Dr. Hiroko Dodge from Oregon State University at Corvallis suggests that ginkgo biloba may improve memory. Dr. Dodge’s research team followed 118 people for three years. These patients were at least 85 years old, healthy, and did not have any signs of memory loss or dementia when the study started. Half of these people took ginkgo biloba, and the other half took a placebo. Throughout the study, a patient’s memory was evaluated using a 5-point scale called the Clinical Dementia Scale, which is commonly used by doctors and researchers to test memory impairment. At the end of the three years, 21 people had developed memory problems or dementia according to this scale, and most of them were in the placebo group. However, the difference between the ginkgo biloba group and the placebo group was not statistically significant. The researchers then did another analysis of their data, focused on the patients who consistently took their ginkgo biloba on a regular basis. The patients taking it regularly had a 70% lower risk of developing dementia, and this difference was statistically significant.
In 2010, German researchers performed a meta-analysis combining nine studies that tested if ginkgo biloba was more effective than placebo in reducing memory loss or Alzheimer’s disease. They found that overall, worsening of memory loss or Alzheimer’s disease was less likely for people taking ginkgo biloba, compared to the people who took a placebo. Although all nine studies found ginkgo biloba to help prevent memory loss, some studies found it to be more effective than others.
The Cochrane Collaborative is a well-respected international group that provides an independent analysis of many studies. A 2009 Cochrane review of 36 studies on whether ginkgo biloba affected memory or dementia found that results were inconsistent. Moreover, of the four studies that were the most recent and better designed studies in the Cochrane review, only one found a benefit from taking ginkgo.
Unfortunately, Dr. Dodge and colleagues found that in addition to the benefits of reducing memory loss, ginkgo biloba also may also increase the risk of strokes. By the end of the three years, seven of the patients taking ginkgo biloba had had strokes, while no patients taking the placebo did. Although the number of patients is small, it does raise concerns. Previous research has shown that ginkgo biloba can increase circulation and reduce the blood’s ability to clot. However, all but one of the strokes recorded in the study were caused by blood clots, so Dr. Dodge and colleague’s observations seem to contradict the expected benefits. A larger study would be needed to find more conclusive evidence of such a risk. A 2008 study by the University of Virginia’s School of Medicine studied 3,069 patients who took either ginkgo biloba or placebo. The men and women with heart disease were at greater risk of developing dementia if they took ginkgo biloba than if they took placebo. In 2013, the Center for Science in the Public Interest (CSPI) issued a warning to consumers advising against taking ginkgo biloba, because it found clear evidence that ginkgo biloba extract caused cancer in animals.
Should I take Ginkgo Biloba?
Like most herbal products, nobody knows exactly how ginkgo biloba works. Even with so many studies, we just don’t know if ginkgo biloba is likely to be good or bad for individual patients. Meanwhile, we agree with the Center for Science in the Public Interest that it makes sense to avoid the drug, since the benefits are unclear and the risks could be substantial.
All NCHR articles are reviewed and approved by Dr. Diana Zuckerman and other senior staff.
- Dodge, HH, Zitzelberger, T, Oken, BS, Howieson, D, Kaye, J (2008). A randomized placebo-controlled trial of Ginkgo biloba for the prevention of cognitive decline. Neurology 70(19),1809-1817. doi: 10.1212/01.wnl.0000303814.13509.db
- Winmann S, Roll S, Schwarzbach C, Vauth C, & Willich SN. Effects of ginkgo biloba in dementia: systematic review and meta-analysis. BMC Geriatrics. 2010, 10:14. doi:10.1186/1471-2318-10-14
- Birks, J, Grimley Evans, J (2009). Ginkgo biloba for cognitive impairment and dementia. Cochrane Database Syt Rev (1):CD003120. doi: 10.1002/14651858.CD003120.pub3 Accessed May 2, 2013.
- Hofferberth B. The effect of Ginkgo biloba extract on neurophysiological and psychometric measurement results in patients with psychotic organic brain syndrome. A double-blind study against placebo (Einfluss von Ginkgo biloba-Extrakt auf neurophysiologische und psychometrische Messergebnisse bei Patienten mit hirnorganischem Psychosyndrom. Eine Doppelblindstudie gegen Plazebo). Arzneimittelforschung 1989;39(8):918-22.
- DeKosky, Steven T.; Williamson, Jeff D.; Fitzpatrick, Annette L.; Kronmal, R. A.; Ives, D. G.; Saxton, J. A.; Lopez, O. L.; Burke, G. et al. (2008). “Ginkgo biloba for Prevention of Dementia”. The Journal of the American Medical Association 300 (19): 2253–2262.doi:10.1001/jama.2008.683. PMC 2823569.PMID 19017911.
- Consumers Urged to Avoid Ginkgo in Wake of New Cancer Concerns. April 18, 2013. Center for Science in the Public Interest. Retrieved from http://www.cspinet.org/new/201304181.html(Accessed August 8, 2013)