Marihuana usage is associated with a life-style that involves earlier and more frequent sexual activity. Marihuana usage does not affect human male testosterone levels significantly, but does adversely affect sperm production. Animal studies have not found consistent changes in weights of male sexual organs but have corroborated the adverse effects of cannabinoid compounds on sperm production. The biological significances of these effects on sperm production are unclear, however, since there is no evidence that human marihuana users or male animals given cannabinoid compounds are less fertile or are at risk for dominant lethal mutations. Cannabinoid compounds reliably inhibit ovulation in animals and are associated with depressed luteinizing hormone (LH) levels in both female and male animals. The decreased LH levels appear to be due to both hypothalamic and ovarian sites of action. Treatment with cannabinoid compounds is also associated with lower testosterone levels in male and lower prolactin levels in female animals. Effects on progesterone levels are inconclusive. Cannabinoid compounds do not possess estrogenic activity. Despite some consistencies in the data in virtually every study conducted with animals, there has been a basic confounding between direct drug action and secondary effects resulting from drug-induced decreases in food and water consumption and attendant weight loss. Almost all of the adverse effects of cannabinoid exposure on reproductive organs can be attributed to these secondary effects.