As of 2014, ginkgo biloba leaves are generally considered safe, but individuals with a history of heart attack, stroke, clotting disorders, epilepsy or diabetes should avoid them. Ginkgo consumed in large doses may cause side effects, including bleeding, nausea, dizziness and headaches. Ginkgo leaves are not safe for children.
Ginkgo is distributed in two forms: extracts and dried leaves. The extract of ginkgo leaves is preferred because it allows doctors to standardize the amount of ginkgo administered and reduce toxic chemicals, called alkylphenols and ginkgotoxins, that can lead to numerous unpleasant side effects. Terpenoids, the chemicals in ginkgo that are considered healthy, dilate the user's blood vessels and increase the flow of oxygen and nutrients throughout the body, but they prevent clotting, which can lead to complications for people suffering from certain health problems. Individuals should consult a healthcare professional prior to taking ginkgo.