The side effects of ginkgo biloba leaf extract are generally mild and include dizziness, headache, upset stomach, allergic skin reactions, constipation and forceful heartbeats, as listed by WebMD. The fruit and pulp of ginkgo biloba can irritate mucous membranes and cause severe allergic skin reactions in some individuals.
Ginkgo biloba's blood-thinning capability decreases the blood's ability to clot, which may cause excessive bleeding or bruising, according to WebMD. Several cases of bleeding after surgery, bleeding of the eye and bleeding in the brain have been associated with ginkgo biloba use. Animal research suggests that very high doses of ginkgo biloba leaf extract increase the risk of liver and thyroid cancer. However, more research is needed as of 2015 to determine whether this applies to humans. Individuals are more prone to an allergic reaction to ginkgo if they are allergic to mango rind, poison oak or poison sumac.
Fresh ginkgo seeds are poisonous and can cause seizures and death, and roasted seeds can cause weak pulse, seizures, difficulty breathing and loss of consciousness if an individual consumes more than 10 per day, as confirmed by WebMD. Women who are pregnant or breast-feeding should avoid ginkgo biloba as it may cause early labor. The substance may also interfere with diabetes management, increase the risk of seizures and interfere with a woman's ability to get pregnant.