How Ginkgo works
Ginkgo (Ginkgo biloba) extract is used in Europe and North America to treat dementia and other neurodegenerative diseases. Most commercially available preparations are standardized to two active ingredients: flavone glycosides and terpenoids. The flavonoid constituent is a strong antioxidant and is believed to have a general neuroprotective benefits. The terpenoid fraction interferes with platelets and helps individuals recover following a stroke by decreasing the risk of blood clots in the brain and reducing nerve cell death associated with stroke. Constituents of Ginkgo may also inhibit neurotoxicity and nerve cell death caused by nitric oxide.
Ginkgo may improve cognitive functioning in both healthy and cognitively impaired non-demented adults
Two placebo-controlled trials found that a compound herbal product containing both Ginkgo biloba (160 or 320 mg) and Panax ginseng (400 mg) resulted in transient improvement in recall performance in healthy adults. Enhanced cognitive functioning appears to reach its peak approximately 6 hours after the herbal preparation is taken. Preliminary findings suggest that combining Ginkgo with another traditional Chinese herbal, dangshen (Codonopsis pilosula), may improve cognitive performance in healthy adults more than either herbal alone. A meta-analysis of 11 clinical trials on standardized ginkgo extracts in elderly cognitively impaired individuals who did not meet full criteria for dementia suggested consistent cognitive enhancing effects.
Inconsistent findings for Ginkgo as a treatment of dementia
Early systematic reviews of randomized controlled trials on ginkgo in dementia concluded that ginkgo preparations in doses between 120 and 600 mg per day taken over several weeks to 1 year result in modest improvements in memory, general cognitive functioning, and activities of daily living in mild to moderate Alzheimer dementia and multi-infarct dementia. However, a systematic review of all randomized controlled trials published up to 2006 on ginkgo in the treatment of dementia and other types of acquired cognitive impairment found inconsistent evidence, noting that early trials were generally small or methodologically flawed, including the absence of standardized preparations and the use of different dementia rating scales across studies. In a 24-week, double-blind placebo-controlled trial, patients with mild to moderate dementia were randomized to a standardized ginkgo extract (160 mg per day) versus the cholinesterase inhibitor donepezil (5 mg per day) or placebo. At 24 weeks, patients taking ginkgo and donepezil experienced equivalent improvements in cognitive performance and global functioning. The findings of one study suggest that the rate of overall cognitive decline is moderately slowed in severe dementia.
Ginkgo has safety issues related to interference with normal blood clotting
Ginkgo is generally well tolerated. Mild transient adverse effects include upset stomach, dizziness, and headaches. Cases of spontaneous bleeding have been reported. Ginkgo should be avoided in individuals taking aspirin, or anticoagulants like warfarin, or heparin. G. biloba preparations should be discontinued at least 2 weeks prior to surgery. G. biloba may cause elevation of hepatic enzymes, and there are case reports of possible serotonin syndrome when taken with SSRIs.