Although not rigorously tested, the inhibition of PAF, a desirable effects of Ginkgo biloba, is also the reason for adverse effects. The risk associated with Ginkgo use is bleeding secondary to the inhibition of platelet aggregation. Adverse events have mainly been documented in individual case reports.

One report by Rowin and Lewis in the American Academy of Neurology (1995), is a case of a 33-year-old woman without a significant past medical history who presented with new onset, diffuse headaches.  Over the next 3 months, the headaches increased in severity, and she began having symptoms of diploplia, nausea, and vomiting.  She had no history of trauma, alcohol use, nor bleeding disorders.  Her PCP prescribed ergotamine/caffeine tablets for possible migraines.  Finally, an MRI of the brain was performed and revealed subacute bilateral subdural hematomas with mass effect.  She underwent bilateral burr hole evacuation and her symptoms improved significantly.  It was at this time, that the history of self-prescribed chronic Gingko use was revealed.  She had taken the recommended dosage of 60 mg twice a day for two years.  The only other medications she admitted to taking was acetaminophen.  At this time, her two bleeding times were measured and both were increased at 15 and 9.5 minutes (normal 3.0-9.0 minutes).  She was instructed to discontinue the Ginkgo, and 35 days later for follow-up, the patients bleeding time had normalized to 6.5 minutes, and she remained symptom free.  Her spontaneous subdural hematomas were attributed to her Ginkgo biloba use, and 15 months later she remained headache, symptom, and Ginkgo free.

In 1997, Rosenblatt and Mindel described a case of a 70-year-old man who presented with spontaneous bleeding into the anterior chamber of his eye one week after beginning a self-prescribed regimen of 40 mg, twice a day of concentrated Ginkgo biloba (Ginkoba).  His past medical history was significant for a CABG (coronary artery bypass graft) three years prior, and his only medication was one 325 mg aspirin per day.  The cause of his bleed was attributed to the combination of aspirin and Gingkoba, both of which inhibit platelet aggregation.  He discontinued the Gingkoba, but continued taking the aspirin daily and had no history of further bleeding episodes at three months follow-up.

In 1997 Gilbert published a case report associating the use of Ginkgo biloba with spontaneous intracerebral hemorrhage in a 72-year-old woman who had been taking the 50 mg of the herbal preparation, three times a day for six months. No history of trauma was given.

In 1998, Matthews published a case report in Neurology of a 78-year-old woman who had been stable on Warfarin for five years for chronic atrial fibrillation and sick-sinus syndrome. She had undergone a CABG five years prior and had a history of hypertension and previous myocardial infarction (heart attack). Two months after her daughter started her on Ginkgo biloba, the patient presented to Cardiology clinic with new onset of an inability to feed herself, severe apraxia, and moderate cognitive deficits. A CT scan revealed a left parietal hemorrhage responsible for her hemorrhage. A heart echocardiogram revealed no source of embolus. She was admitted to the hospital and her anticoagulation was allowed to reverse. She continued to have residual deficits from the stroke a month later. It was postulated that the Ginkgo biloba could have had an additive effect with the Warfarin, which has a different mechanism of action, and both may have contributed to the hemorrhage.

In 2001, Age and Aging described two patients with previously well controlled epilepsy, who went on to develop recurrent seizures within two weeks of commencing ingestion of ginkgo biloba extract. Both patients were again seizure-free several months after discontinuation of the herb.

These individual cases by no means offer proof that Ginkgo biloba was the direct cause of the bleeding disorders.  However, the association seems to be strong enough to assume that Gingko biloba may contribute to bleeding.

The use of ginkgo biloba can enhance anticoagulation and antithrombotic therapy.  Ginkgo biloba should not be used by patients who are taking NSAIDs, aspirin, warfarin,  or heparin.