Ginkgo biloba is not a smart drug: an updated systematic review of randomised clinical trials testing the nootropic effects of G. biloba extracts in healthy people

Abstract

Here, we update our earlier systematic review of 2001, which critically evaluated the data from clinical trials to determine whether Ginkgo biloba enhances cognitive function in healthy subjects. Literatures searches of six computerised databases, updated to January 2007, were made for randomised, placebo-controlled, double-blind clinical trials of the effects of standardised Ginkgo biloba (G. biloba) extracts on cognitive function in healthy subjects under the age of 60 years. Trials published in any language were included, and data were extracted independently by the two authors following a standardised protocol. We include 15 randomised clinical trials of which 7 are single-dose studies and 8 are longer term studies with treatment periods ranging from 2 days to 13 weeks. Three single dose studies and 4 longer term studies are newly included. Several of the studies have methodological flaws. A number of the acute studies used multiple outcomes and report positive effects on one or more of these at particular time points with particular doses but these findings are either not replicated, or are directly contradicted by other studies. The evidence from longer term studies is largely negative. Of those studies which measured subjective effects, only one of five acute studies and one of six longer term studies reported any significant positive results. Overall, and in line with our previous conclusions, we have found no convincing evidence from randomised clinical trials for a robust positive effect of G. biloba ingestion upon any aspect of cognitive function in healthy young people, after either acute or longer term administration.

Ginkgo biloba: specificity of neuropsychological improvement—a selective review in search of differential effects

“…1-2). Similar negative evidence is stated in a review on healthy people younger than 60 years in acute as well as chronic administration (Canter and Ernst, 2007). This is again in sharp contrast to a review also examining short-and long-term administration in healthy and cognitively intact adults-'significant positive results in 11 of 16 studies' (Crews et al, 2005;p.…”

“…Following other reviews (Canter and Ernst, 2007), the percentages of these two components in each of the extracts are given in Table 2. The last two colums of Table 2 report significant superiority of ginkgo over placebo in the respective trial or lack of such evidence.…”

“…The basic assumption is that authors of published studies were blind to the function-specific rationale presented here-making a specific bias practically unlikely: there was no reason to assume that an author prefers to report a significant result for one function while ignoring another. Thus, the Bonferroni rationale of correcting for multiple comparisons which is often lacking in this field (Canter and Ernst, 2007) was applied across all trials included into this review. Bonferroni corrections for multiple comparisons were done within each of the cognitive functions: given one score per test and p < 0.05 as significance level, only 5.0 of 100 tests would become significant just by chance.…”

“…A standardized special extract (EGb 761 11 ) is widely prescribed in Europe for the treatment of ageassociated cognitive decline (including dementia; Canter and Ernst, 2007) and different neurosensory and circulatory disorders it became quite popular (tinnitus, vertigo, claudicatio intermittens; cf Birks et al, 2002). Most of the available empirical research was done with this special extract, which is obtained in a multiple-step extraction process, purified to remove harmful accompanying substances, and standardized to 24% ginkgo-flavone glycosides and 6% terpene lactones (ginkgolides, bilobalide), the pharmacologically active constituents (DeFeudis, 1998).…”

Modulation of cognitive performance following single doses of 120 mg Ginkgo biloba extract administered to healthy young volunteers

“…Several placebo-controlled experiments have assessed the effects of single doses of Ginkgo extract on cognitive performance (Elsabagh et al, 2005;Hindmarch, 1986;Kennedy et al, 2000Kennedy et al, , 2002aWarot et al, 1991), although the evidence from these studies is less than compelling (for review see Canter and Ernst, 2007). However, these studies include two (Hindmarch, 1986;Warot et al, 1991) that adopted a balanced cross-over design, but utilised small sample sizes (n ¼ 8 and 12, respectively).…”