Uses and Efficacy
cerebrovascular disease, dementia, and memory enhancement
A systematic review11 of eight randomized, double-blind, placebo-controlled studies concluded that ginkgo had modest effects on improving the symptoms of dementia and cerebral insufficiency equivalent to pharmacologic therapy with ergoloid mesylates (Hydergine). A later meta-analysis surveyed 50 articles to examine the effect of ginkgo on objective measures of cognitive function in patients with Alzheimer's disease.12 [Evidence level A, meta-analysis] Four of these studies met inclusion criteria for adequate clinical trial design. In the 212 subjects in the placebo and ginkgo groups, a significant overall effect size was found that was comparable with the benefits of donepezil (Aricept). Efficacy was measured using the Alzheimer's Disease Assessment Scale-Cognitive subscale (ADAS-Cog) and other standardized measures of cognition.
A review18 of studies of at least six months in duration demonstrated that ginkgo extract and second-generation cholinesterase inhibitors were equally effective in treating mild to moderate Alzheimer's dementia. A systematic review of nine studies on ginkgo use showed a safe and positive effect beyond placebo, but the investigators remained tentative in recommending it for treatment of dementia until better studies are conducted. A Cochrane meta-analysis of 33 trials concluded that ginkgo appears to be safe, and showed promising evidence of improvement of cognition and function among patients who received the herb. However, the three modern trials showed inconsistent results, suggesting that a large trial with modern methodology is needed to answer questions about treatment effects. [Evidence level A, meta-analysis]
One of the studies analyzed in the Cochrane review was a Dutch study of 214 patients over 24 weeks using a medium dosage of ginkgo (160 mg per day), a high dosage of ginkgo (240 mg per day), or placebo in a crossover design. This study failed to show improvement in age-associated memory impairment or mild or moderate dementia in several neuropsychologic and behavior outcome measures. However, this study included patients with age-associated memory impairment rather than just persons with dementia, which may have limited the statistical power of its conclusions about the role of ginkgo in dementia.
A randomized, placebo-controlled trial of the effects of ginkgo in healthy, noninstitutionalized adults without dementia or other known mental deficit found no benefit from six weeks of ginkgo therapy (120 mg per day) on several standardized neuropsychologic measures of memory and learning. However, a study using a similar design with a higher dosage of ginkgo (180 mg per day) showed clinically significant cognitive benefits in healthy persons.
The National Institutes of Health and the National Center for Complementary and Alternative Medicine have sponsored a multi-center, six-year, randomized, two-arm, double-blind, placebo-controlled trial of 2,000 patients. The trial will evaluate the safety and efficacy of ginkgo in preventing dementia and age-related cognitive decline and is currently underway and headed by investigators at the University of Pittsburgh. Another phase III trial is underway at the Oregon Health Sciences Center, Portland, to study the effects of ginkgo on cognitively intact elderly patients older than 85 years, and the effect on their progression to mild cognitive impairment. This study will use volumetric quantitative magnetic resonance imaging measures of brain size and peripheral oxidative markers.
Another indication for ginkgo is intermittent claudication from peripheral vascular disease. A meta-analysis of eight studies concluded that the effects of ginkgo, though statistically significant and positive on increasing pain-free walking, were of modest effect size and questionable clinical relevance. [Evidence level A, meta-analysis] A trial that compared dosages of 120 mg and 240 mg of ginkgo demonstrated a substantial therapeutic benefit on pain-free walking distance with the higher dosage. Two placebo-controlled trials, with a total of 190 patients, showed improved walking distance and decreased pain in patients with peripheral vascular disease.
Another common indication for ginkgo is tinnitus. A recent study of 1,121 subjects conducted using questionnaires and telephone interviews, without the use of standard audiometric testing as an outcome measure, failed to show a benefit of ginkgo in the treatment of tinnitus. Another randomized, placebo-controlled trial of 103 patients showed 50 percent of patients with new-onset tinnitus had improvement or disappearance of symptoms in
70 days compared with 119 days to improvement in those receiving placebo. A review31 of five heterogenous randomized controlled trials concluded that extracts of ginkgo biloba are moderately effective in treating tinnitus.
Studies have shown positive results from the use of ginkgo for the following conditions: sexual dysfunction secondary to the use of selective serotonin reuptake inhibitors, mountain sickness and decreasing vasoactivity in response to cold, macular degeneration, asthma, and hypoxia. The World Health Organization has recommended the use of ginkgo in Raynaud's disease, acrocyanosis, and post-phlebitic syndrome.
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