A systematic review of research investigating the physiological and psychological effects of combining Ginkgo biloba and Panax ginseng into a single treatment in humans: Implications for research design and analysis.

BACKGROUND AND PURPOSE: The traditional herbal supplements Panax ginseng and Ginkgo biloba are self-medicated by members of the general public and prescribed by healthcare professionals in some EU countries for numerous health complaints. Clinical evidence is mixed and mechanisms of action are not fully understood. There is clinical interest into the synergistic effects of combining both herbs.

METHODS: We systematically review the literature investigating the effects of combination treatments on physiological and psychological outcomes in humans. We identified all studies meeting inclusion criteria: (a) written in English; (b) peer-reviewed; (c) conducted in humans; (d) including either a proprietary Panax ginseng/Ginkgo biloba treatment or a study preparation containing both; (e) placebo-controlled; (f) utilizing standardized extracts. We critically discuss each trial; calculate standardized effect sizes where possible and provide recommendations for research design and analysis.

RESULTS: Eight studies were identified and all investigated a proprietary combination treatment, Gincosan® . Studies are of high quality and robust; however, practice effects, choice of statistical model, and reliance upon null-hypothesis significance testing hinder generalized estimates of effect. The most consistent results are benefits to aspects of the circulatory/cardiovascular system in patient populations and "secondary memory" performance in patient and healthy populations. Two studies demonstrate synergy in healthy populations following a single dose; however, synergy in patient populations and following repeated dosing has not yet been directly tested.

CONCLUSIONS: A Panax ginseng and Ginkgo biloba combination treatment can improve aspects of physiological and cognitive function in humans; however, evidence for synergy requires further investigation and future research should directly investigate synergy following repeated dosing.