Ginkgo Biloba and Aspirin Both Reduce Platelet Clumping. Together, the Effect Adds Up
Ginkgo has independent antiplatelet activity. Added to aspirin, the combined effect on bleeding time is greater than either alone. The case reports and mechanism explained.
Low-dose aspirin is taken by millions of people daily for cardiovascular protection. Ginkgo biloba is taken by many of the same people for memory and circulation. The two are often assumed to be independent. At the level of platelet function, they are not.
Two antiplatelet mechanisms
Aspirin works by irreversibly inhibiting cyclooxygenase-1 (COX-1), an enzyme that platelets use to produce thromboxane A2, a compound that promotes platelet aggregation and blood vessel constriction. With COX-1 blocked for the platelet’s lifetime, the platelet is permanently less sticky. Low doses are sufficient to achieve this effect.
Ginkgo biloba’s antiplatelet activity works through a different pathway. Ginkgolide B, one of ginkgo’s active compounds, inhibits platelet activating factor (PAF), a lipid mediator that normally binds to receptors on platelets and triggers aggregation. By blocking PAF binding, ginkgo reduces a second distinct pathway through which platelets are activated.
Because the two mechanisms are independent, their effects on overall platelet function are additive rather than redundant. Together, they produce greater impairment of clot formation than either alone.
Case reports
A case reported by Rowin and Lewis in 1996 described a patient who developed spontaneous bilateral subdural haematomas, a serious and potentially fatal form of bleeding into the space surrounding the brain, while taking ginkgo biloba with no other antiplatelet medication.
Subsequent case reports and reviews documented similar bleeding events in patients combining ginkgo with aspirin or other NSAIDs. The pattern was consistent enough that haematology and clinical pharmacology review articles began including ginkgo as a supplement requiring caution in patients on antiplatelet therapy.
Who should be cautious
People on daily low-dose aspirin for cardiovascular disease — already at somewhat elevated bleeding risk as a result of the medication — add additional risk by taking ginkgo. The concern is particularly relevant at higher doses of ginkgo and for people who already have other bleeding risk factors.
The interaction is also relevant for people taking NSAIDs (ibuprofen, naproxen) regularly, not just aspirin, as NSAIDs also have COX-inhibiting antiplatelet effects.
A note on dose
Most of the research on ginkgo’s antiplatelet activity used standardised extracts (EGb 761) at doses of 120–240mg per day. The interaction with aspirin is considered most significant at doses in this range. Casual or occasional use of lower-dose preparations may carry lower risk, though the interaction is still present mechanistically.
Reference
- Rowin J, Lewis SL. "Spontaneous bilateral subdural hematomas associated with chronic Ginkgo biloba ingestion." Neurology, 1996. PubMed 11140003
