Warnings, Interactions, Adverse Effects
During the past 20 years, an estimated 2 billion daily doses (120 mg) of ginkgo have been sold. The most important potential clinical problem with ginkgo is caused by its inhibition of the platelet-activating factor; this makes the use of ginkgo in conjunction with warfarin (Coumadin), aspirin, or other antiplatelet agents a matter of clinical judgment. A recent safety study of the interaction of ginkgo and warfarin showed no change in the international normalized ratio. Ginkgo should be discontinued between 36 hours and 14 days before surgery, based on either pharmacokinetics or consensus opinion.
Herbal medications that may increase the risk of bleeding if used concurrently with ginkgo include the following: feverfew, garlic, ginseng, dong quai, red clover, and other natural coumarins. Several case reports of bleeding complications associated with ginkgo use include subdural hematoma, subarachnoid hemorrhage, intracerebral hemorrhage, and hyphema; the causality of these events has not been established. One case report discussed an elderly patient who developed elevated blood pressure while taking a thiazide diuretic and ginkgo. The patient's blood pressure returned to normal when both substances were discontinued. This reaction is paradoxical in light of the known pharmacologic actions of these agents.
The unprocessed ginkgo leaf contains ginkgolic acids that are toxic. Hypersensitivity to ginkgo preparations is a contraindication to use. Ginkgo is generally well tolerated, with side effects being rare, usually mild, and including nausea, vomiting, diarrhea, headaches, dizziness, palpitations, restlessness, weakness, or skin rashes. Although no studies have been performed to support any restrictions on the use of ginkgo during pregnancy or lactation, it seems prudent not to administer ginkgo in the absence of any data.
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