Ginkgo (Ginkgo biloba, Ginkgoaceae) is most commonly used to treat dementia and peripheral claudication. Many reviews have reported that it is generally “safe under conditions of usual intake.” There is a growing concern that ginkgo may be contraindicated under conditions that may predispose individuals to bleeding disorders. This would occur, for example, in patients taking anticoagulants or thrombolytic agents. The purpose of this study was to determine whether a high dose of ginkgo would affect platelet function in patients taking a daily dose of 325 mg aspirin (platelet aggregation inhibitor).

Adults with established peripheral artery disease (PAD) or a risk for PAD due to either family history of cardiovascular disease (CVD) or elevated CVD risk factors such as diabetes, hypercholesterolemia, or hypertension were recruited from the local community (Stanford University Medical School, Stanford, CA) to participate in this randomized, double-blind, placebo-controlled study. Participants (n = 67) received either placebo or 300 mg/day of the ginkgo extract EGb 761 (Dr. Willmar Schwabe, Karlsruhe, Germany; Ginkgold^®, Nature’s Way, Springville, Utah) for 4 weeks. EGb 761 contains 24% ginkgo flavone glycosides and 6% terpene lactones. All participants also took 325 mg/day aspirin. Aspirin treatment was initiated 2 weeks prior to EGb 761 administration. Patients recorded daily bleeding or bruising in a log. Blood samples were collected to analyze platelet function.

Treatment adherence was excellent, with participants consuming more than 90% of the tablets. Twenty-six participants reported attendant symptoms, 11 in the EGb 761 group and 15 in the placebo group (P = 0.4). Unusual bleeding and/or nosebleeds were reported by 5 in the EGb 761 group and 4 in the placebo group. Upset stomach was reported by 6 in the EGb 761 group and 5 in the placebo group. The pre-study to end-study change in time for clotting was not significantly different between groups. Platelet aggregation was assessed via 4 classical tests. With all 4 tests, there was no significant difference from pre-study to end-study in platelet aggregation between the EGb 761 and placebo groups.

The authors conclude that adding 300 mg/day of EGb 761 to daily aspirin therapy in this patient population did not have a detectable effect on platelet function as assessed by 2 standard methods. The authors state that a limitation of the study was that additional measures of platelet function and coagulation were not assessed in this study. Also, a participation of larger number of participants would have permitted greater sensitivity to detect small inter-group differences. It should also be noted that this study used a sample size that was larger than many other published studies.

This study shows that a relatively high dose of EGb 761 combined with daily aspirin did not have clinically or statistically detectable impact on indices of coagulation examined over 4 weeks. Considering that this study had exemplary design, execution, and synopsis, and employed tests commonly used in clinical practices, the conclusion is convincing.

—Heather S. Oliff, PhD