Int J Clin Pharmacol Ther. 2003 Aug; 41(8): 354-7.

Multiple n = 1 trials in the identification of responders and non-responders to the cognitive effects of Ginkgo biloba.

Canter PH, Ernst E.

Complementary Medicine, Peninsula Medical School, Universities of Exeter and Plymouth, Exeter, Devon, UK. peter.canter@pms.ac.uk

OBJECTIVE: A pilot study to assess multiple crossover n = 1 trials with verum/placebo discrimination as the outcome measure as a means of identifying responders and non-responders to the acute nootropic effect of Ginkgo biloba (G. biloba) among healthy volunteers. METHOD: Multiple double-blind, placebo-controlled n = 1 trials with 8 treatments in randomized order and separated by minimum washout periods of 7 days. Treatments were acute 120 mg doses of G. biloba extract (GK501) or undistinguishable placebo. The frequency distribution of correct scores for verum-placebo discrimination was compared with the binomial distribution to identify putative responders, who were then tested for consistency of performance over a further 8 treatments. RESULTS: The frequency distribution of scores (n = 11) was bimodal and a discontinuity defined 3 putative responders and 2 putative negative responders for re-test. Two of the putative responders again performed at above chance level and the probability of achieving their scores or better by chance was 0.013 and 0.052. CONCLUSIONS: n = 1 trials with verum/placebo discrimination as outcome are a promising method for exploring response heterogeneity to treatments with a subjective effect. Preliminary evidence suggests that there are responders and non-responders to an acute G. biloba treatment among healthy subjects.