Testosterone levels were reportedly lowered by “chronic intensive marijuana use” in one 1974 study. These findings have not been substantiated by subsequent research. Two studies concluded that regular administration of cananbinoids reduced testosterone levels in rats, but a review of those studies by Leo Hollister concluded that no significant effect on testosterone or fertility was found. There is no epidemiological evidence that cannabis users are at risk of lowered testosterone levels.
Related sections: Fertility.