Focus on Alternative and Complementary Therapies
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Focus Alternat Complement Ther©2005 Pharmaceutical Press
Focus Altern Complement Ther 2003; 8: 130
(1) To test if there are responders and non-responders to the nootropic effect of Ginkgo biloba among healthy volunteers; (2) to assess multiple crossover n = 1 trials as a method to identify responders.
Double-blind, placebo-controlled, randomised n = 1 trials with eight treatments (acute 120-mg dose of G. biloba extract or indistinguishable placebo) separated by minimum washout periods of 7 days. The frequency distribution of correct scores for verum-placebo discrimination was compared with the binomial distribution to identify putative responders scoring above chance level, and was inspected for skew or bimodality.
The frequency distribution of scores (n = 11) was bimodal and a discontinuity defined three putative responders (6/8 or 7/8 correct). The three putative responders and two putative negative responders (2/8 correct) received a further eight treatments. Consistency of performance was shown only by two of the putative responders that performed at above-chance level in the follow-on but not markedly so (5/8 correct). The probability of achieving these combinations of scores or better over the two trials by chance is 0.013 and 0.052. Correct identification of verum was most frequently associated with the subjective cue of improved concentration.
Preliminary evidence suggests that there may be responders and non-responders to an acute 120-mg dose of G. biloba extract. A very cautious estimate is that responders constitute around 20% of a healthy population. A larger trial would allow statistical comparison of expected and actual scores and would reveal whether the bimodality in scores is real or an artefact of the small sample size. The n = 1 trial is a promising method for differentiating responders and non-responders to any treatment where a subjective effect is expected but protocols must be carefully designed to prevent the use of guessing strategies that could increase false positives.
