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Ginkgo and memory.

To the Editor: Dr Solomon and colleagues reported that 6 weeks of treatment with Ginkgo biloba failed to improve performance on standardized neuropsychological tests of learning, memory, attention, and verbal ability in healthy elderly adults without cognitive impairment. The authors argue that clinical findings to date have not supported claims that ginkgo improves cognitive efficiency. Their study, however, is not directly comparable with prior studies, which have varied significantly in terms of trial durations, predictor and outcome measures used, and the type of cohort tested. Moreover, the authors do not mention several methodologically comparable studies, including our 1-month trial, which have reported selective improvements in neuropsychological status in young adults and healthy older subjects treated with ginkgo. In addition, we believe that outcome trials should use cognitive tests that are sensitive to ginkgo’s pharmacologic mode of action in the brain. It has been suggested that ginkgo’s effects may be explained by its modulatory influence on the human cholinergic system. Furthermore, ginkgo may have remediating effects in patients with mild to moderate Alzheimer disease, a disorder putatively associated with cholinergic dysfunction. The selection of tests by Solomon et al and others, while validated as clinical measures of brain and behavioral function, may not be suitable to outcome studies of complementary therapies such as ginkgo, which generally produce only a mild to moderate benefit with continued use. Finally, as is often the case with pharmacologic studies in healthy participants, cognitive change may in part relate to individual differences in baseline cognitive and intellectual ability. Our study of ginkgo found that young adults categorized into a “low cognitive ability” group improved on certain tests when compared with those with a “high cognitive ability.” We believe that further large-scale trials are needed to establish ginkgo’s efficacy as a cognitive enhancer.