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

Extracts of Ginkgo biloba are widely used for the treatment of cognitive impairment. Whereas reviews have focused on the question whether ginkgo is effective to enhance cognition in general, little is known about specificity of improvement. This might be crucial for future trials, thus enabling hypotheses about sensitive outcome measures. Therefore, this article summarizes such information, i.e. neuropsychological effects of chronic administration of ginkgo in healthy and cognitively impaired subjects of any age. Objective psychometric test results were considered if they reflected distinct cognitive functions from randomized controlled group-studies (RCT). We reviewed 29 RCTs yielding 209 placebo-drug comparisons of psychometric scores in four different cognitive domains comprising 14 sub-functions. Whereas little specific information can be obtained from trials for treatment of dementia, a pattern of pharmacological actions on cognitive processes emerges here from studies for mild cognitive impairment (MCI), depression, multiple sclerosis and healthy young and elderly subjects. There is consistent evidence that chronic administration improves selective attention, some executive processes and long-term memory for verbal and non-verbal material. Further trials should be more comprehensive as there are few data available on some cognitive functions and psychometric flaws in the selection of tests and the interpretation of their results favouring predominantly beta-errors. Thus, though this pattern is encouraging it also asks for a cautious interpretation to date.