Objective: To determine the effect of treatment with Ginkgo biloba ext
ract on objective measures of cognitive function in patients with Alzh
eimer disease (AD) based on formal review of the current literature. M
ethods: An attempt was made to identify all English and non-English-la
nguage articles in which G biloba extract was given to subjects with d
ementia or cognitive impairment. Inclusion criteria for the meta-analy
sis were (1) sufficiently characterized patients such that it was clea
rly stated there was a diagnosis of AD by either Diagnostic and Statis
tical Manual of Mental Disorders, Revised Third Edition, or National I
nstitute of Neurological Disorders and Stroke-Alzheimer's Disease and
Related Disorders Association criteria, or there was enough clinical d
etail to determine this by our review; (2) clearly stated study exclus
ion criteria, ie, those studies that did not have stated exclusions fo
r depression, other neurologic disease, and central nervous system-act
ive medications were excluded; (3) use of standardized ginkgo extract
in any stated dose; (4) randomized, placebo-controlled and double-blin
d study design; (5) at least 1 outcome measure was an objective assess
ment of cognitive function; and (6) sufficient statistical information
to allow for meta-analysis. Results: Of more than 50 articles identif
ied, the overwhelming majority did not meet inclusion criteria, primar
ily because of lack of clear diagnoses of dementia and AD. Only 4 stud
ies met all inclusion criteria. In total there were 212 subjects in ea
ch of the placebo and ginkgo treatment groups. Overall there was a sig
nificant effect size of 0.40 (P<.0001). This modest effect size transl
ated into a 3% difference in the Alzheimer Disease Assessment Scale-co
gnitive subtest. Conclusions: Based on a quantitative analysis of the
literature there is a small but significant effect of 3- to 6-month tr
eatment with 120 to 240 mg of G biloba extract an objective measures o
f cognitive function in ED. The drug has not had significant adverse e
ffects in formal clinical trials but there are 2 case reports of bleed
ing complications. In AD, there are limited and inconsistent data that
preclude determining if there are effects on noncognitive behavioral
and functional measures as well as on clinician's global rating scales
. Further research in the area will need to determine if there are fun
ctional improvements and to determine the best dosage. Additional rese
arch will be needed to define which ingredients in the ginkgo extract
are producing its effect in individuals with AD.