There is some contention about the benefits of ginseng for improving memory, concentration and learning (Persson et al 2004). Well-controlled clinical trials are lacking and variations in dosage and standardisation may affect study results.
Some studies have demonstrated that ginseng improves the quality of memory and associated secondary memory (Kennedy et al 2001 a). In a randomised, placebo-controlled, double-blind, balanced crossover study of healthy, young adult volunteers, 400 mg ginseng was shown to improve secondary memory performance on a Cognitive Drug Research computerised assessment battery and two serial subtraction mental arithmetic tasks. Ginseng also improved attention and the speed of performing the memory tasks (Kennedy et al 2002). In a later double-blind, placebo controlled, balanced, cross-over study of 30 healthy young adults, acute administration of ginseng (400 mg) was again shown to improve speed of attention (Sunram-Lea etal 2005).
In a double-blind, placebo-controlled study of healthy young subjects, ginseng extract (G11 5) improved accuracy and slowed responses during one of two computerised serial subtraction tests (Serial Sevens), and it was also shown to improve mood during these tasks (Kennedy et al 2001 b).
In a double-blind, randomised, placebo-controlled 8-9-week trial standardised ginseng extract 400 mg was found significantly to improve abstract thinking (P < 0.005) and reaction time (not significant) in 112 healthy subjects over 40 years of age. Ginseng was found not to affect concentration or memory (Sorensen & Sonne 1996).
In clinical practice Korean ginseng and Ginkgo biloba are frequently used in combination for cognitive benefits. Combining ginseng with ginkgo dramatically improves memory, concentration and speed of completing mental tasks (Kennedy et al 2001 a, Scholey & Kennedy 2002). In clinical trials ginseng directly modulates cerebroelectrical activity on EEG recordings to a greater extent than Ginkgo biloba (Kennedy etal 2003).
In a double-blind, placebo-controlled study, post-menopausal women aged 51-66 years were randomly assigned to 12 weeks' treatment with a combination formula containing 120 mg Ginkgo biloba and 200 mg Panax ginseng (n = 30), or matched placebo (n = 27). The combination appeared to have no effect on mood or cognition after 6 and 12 weeks; however, these doses may be too low (Hartley et al 2004). According to other trials it would appear that doses of 400-900 mg of ginseng are required for best results and 200 mg doses have been associated with Ginseng—Korean 560
'cognitive costs', slowing performance on attention tasks (Kennedy & Scholey 2003).
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