Effects of Panax ginseng and Panax quinquefolius on Cognitive Function: A Systematic Review

Ginseng has a longstanding reputation as an adaptogen, antistress agent and cognitive enhancer. We conducted a systematic review of randomised controlled studies into the cognitive effects of ginseng in non-clinical populations. The initial search captured 1802 records, of which fourteen articles fulfilled the inclusion criteria and were included in this review. The majority of the studies (N = 11) examined the effects of standardized extracts of Panax ginseng (Asian ginseng), with most (N = 8) using a standardised extract. The other three used a standardised extract of Panax quinquefolius (American ginseng). All but one study included acute assessment ranging from 1 h to 6 h post-administration. Four studies included a ‘chronic’ assessment ranging from 8 days to 12 weeks, three of which included ‘acute-on-chronic’ evaluations. Overall, the effects of P. ginseng tended to benefit accuracy of secondary memory (although there was evidence of a speed accuracy trade-off for specific doses), and to some degree attentional processes. P. quinquefolius had a more positive impact on attentional measures and working memory/executive functions. These effects are likely due to differences in ginsenoside profiles and other components via action on numerous systems, including neurotransmitter systems and glucocorticoid and estrogen receptors. Although there were some methodological consistencies across studies, different cognitive measures and extracts were utilised. Notably, the studies which did not specify the ginsenoside constituents of the extract used did not report cognitive benefits, emphasising the need for standardisation and characterisation.