银杏药物一直被认为是有效治疗老年痴呆症的药物。然而，最近科学家们通过实验证明此类药物对老年痴呆症的治疗是没有效果的。

University of Virginia, Charlottesville的Steven T. DeKosky, M.D.及其同僚对银杏预防痴呆症的有效性进行了评估。该研究是一项随机的有安慰剂作为对照的临床试验，研究的时间在2000年与2008 年之间，其中位（即中点）随访时间为6.1年。该试验包括3069位社区的自愿者，其年龄为75岁或以上。在研究开始的时候，他们中包括认知功能正常者（n = 2,587）或认知功能轻度损害者（MCI; n = 482）。这些人每隔6个月接受一次有关痴呆症的评估。这些参与者或是接受每日2次剂量为120毫克的银杏提取物（n = 1,545）或是接受安慰剂（n = 1,524）。

研究人员发现，在实验干预阶段，有523名参与实验者被诊断患有痴呆症，其中246人（占16.1%）来自安慰剂组，277人（占17.9%）来自银杏治疗组。在全部的痴呆症病例中，有92%被归类为可能或很可能的AD，或有脑部血管疾病证据的AD。痴呆症和阿兹海默型痴呆症的总体发病率在银杏组与安慰剂组中没有明显的区别。银杏对MCI的受试者进展为痴呆症的速度也没有影响。

文章的作者写道：“基于这一试验的结果，银杏不应该被推荐作为预防痴呆的治疗手段。”

JAMA. 2008;300(19):2253-2262.

Ginkgo biloba for Prevention of Dementia

Steven T. DeKosky, MD; Jeff D. Williamson, MD, MHS; Annette L. Fitzpatrick, PhD; Richard A. Kronmal, PhD; Diane G. Ives, MPH; Judith A. Saxton, MD; Oscar L. Lopez, MD; Gregory Burke, MD; Michelle C. Carlson, PhD; Linda P. Fried, MD, MPH; Lewis H. Kuller, MD, DrPH; John A. Robbins, MD, MHS; Russell P. Tracy, PhD; Nancy F. Woolard; Leslie Dunn, MPH; Beth E. Snitz, PhD; Richard L. Nahin, PhD, MPH; Curt D. Furberg, MD, PhD; for the Ginkgo Evaluation of Memory (GEM) Study Investigators

Context  Ginkgo biloba is widely used for its potential effects on memory and cognition. To date, adequately powered clinical trials testing the effect of G biloba on dementia incidence are lacking.

Objective  To determine effectiveness of G biloba vs placebo in reducing the incidence of all-cause dementia and Alzheimer disease (AD) in elderly individuals with normal cognition and those with mild cognitive impairment (MCI).

Design, Setting, and Participants  Randomized, double-blind, placebo-controlled clinical trial conducted in 5 academic medical centers in the United States between 2000 and 2008 with a median follow-up of 6.1 years. Three thousand sixty-nine community volunteers aged 75 years or older with normal cognition (n = 2587) or MCI (n = 482) at study entry were assessed every 6 months for incident dementia.

Intervention  Twice-daily dose of 120-mg extract of G biloba (n = 1545) or placebo (n = 1524).

Main Outcome Measures  Incident dementia and AD determined by expert panel consensus.

Results  Five hundred twenty-three individuals developed dementia (246 receiving placebo and 277 receiving G biloba) with 92% of the dementia cases classified as possible or probable AD, or AD with evidence of vascular disease of the brain. Rates of dropout and loss to follow-up were low (6.3%), and the adverse effect profiles were similar for both groups. The overall dementia rate was 3.3 per 100 person-years in participants assigned to G biloba and 2.9 per 100 person-years in the placebo group. The hazard ratio (HR) for G biloba compared with placebo for all-cause dementia was 1.12 (95% confidence interval [CI], 0.94-1.33; P = .21) and for AD, 1.16 (95% CI, 0.97-1.39; P = .11). G biloba also had no effect on the rate of progression to dementia in participants with MCI (HR, 1.13; 95% CI, 0.85-1.50; P = .39).

Conclusions  In this study, G biloba at 120 mg twice a day was not effective in reducing either the overall incidence rate of dementia or AD incidence in elderly individuals with normal cognition or those with MCI.