A systematic review on natural medicines for the prevention and treatment of Alzheimer's disease with meta-analyses of intervention effect of ginkgo.

We performed a systematic review to evaluate the efficacy of natural medicines for the treatment of Alzheimer's disease (AD) in randomized controlled trials (RCTs). Disease-specific and intervention terms were searched in MEDLINE, EMBASE, the Cochrane Library and PsycINFO to identify RCTs for the AD intervention of natural medicines, and searched for literatures in English language. The RCTs compared natural medicines and either placebo or orthodox medication in AD patients. The quality of literature was evaluated by Jadad's score and the Cochrane assessing tool to reduce the risk of bias. Meta-analysis and the heterogeneity of results across the trials were performed. Out of the literatures, 21 clinical reports were included in this review that satisfied the particular selection criteria. Apart from Ginkgo, other treatments we came across had minimal benefits and/or the methodological quality of the available trials was poor. The meta-analyses showed that Ginkgo had better outcomes than the placebo, with the standardized mean difference (SMD) between Ginkgo and the placebo on cognition being -1.62 (95% CI: -2.69 to -0.56) and on activities of daily living being -1.55 (95% CI: -2.55 to -0.55), with the existence of significant heterogeneity across studies. The meta-analysis for assessing the prevention effect of Ginkgo against AD suggested that risk ratio (RR) is 1.06 (95% CI: 0.92 to 1.22) between Gingko and the placebo, with no significant heterogeneity across studies (test for heterogeneity, p = 0.49). Our results suggest that Ginkgo may help established AD patients with cognitive symptoms but cannot prevent the neurodegenerative progression of the disease.