An anecdotal report of gynecomastia in chronic cannabis smokers [1] stimulated research into the effect of cannabis on male hormones [2,3]. A causal association between cannabis and gynecomastia was hypothesized based on the structural similarity of tetrahydrocannabinol (THC) and estradiol. Moreover, tetrahydrocannabinol was shown to directly stimulate development in rat breast tissue [4]. Although laboratory investigations on human subjects provided conflicting results regarding the effects of cannabis use on testosterone levels [2,3], one study failed to demonstrate any influence of intensive cannabis use on prolactin levels [2]. The present report is a case-control study of gynecomastia in a military population-US Army soldiers in Nuremberg, Germany-where the incidence of cannabis use was nearly 50 per cent [5,6].
