PIP: The reproductive system is considered to be particularly vulnerable to the effects of drugs. Hypothalamic neurotransmitters are sensitive to drugs that alter their synthesis, release, or action; disruption of these pathways changes the levels or patterns of secretion of the pituitary gonadotropins. Drugs also exert direct action on the gonadal functions of androgen production and spermatogenesis. Drugs that decrease testosterone levels produce a multitude of effects on male reproduction. Neuropharmacologic agents that either inhibit central nervous system (CNS) activities (e.g., analgesics, anesthetics, sedatives, tranquilizers) or stimulate CNS activities (e.g., antidepressants, stimulants, hallucinogens) modify the hypothalamic-pituitary control of the gonadotropins and prolactin. The changes in luteinizing hormone, follicle-stimulating hormone, and prolactin result in changes in libido, impotence, inability to ejaculate, testicular swelling, and gynecomastia. Narcotic drugs exert their primary effect on the hypothalamic-pituitary axis and their secondary effects on the gonads and sex accessory organs. Narcotics decrease gonadotropin secretion and stimulate prolactin secretion, both of which are inhibitory to male sexual function. With marijuana, the primary drug effect is at the level of the hypothalamus, with subsequent effects on gonadotropins and testosterone. Additional studies are needed on the association of marijuana with disruption of reproduction to resolve conflicing findings. The drugs most likely to affect suxual function are those that act on the sympathetic and parasympathetic systems. Antihypertensive drugs are likely to interfere with autonomic transmission, resulting in impotence or failure of ejaculation. However, it is difficult to determine whether this increased incidence of impotence is entirely a drug side effect of a complication of blood pressure changes. Chemotherapeutic agents, especially anticancer drugs, can cause prolonged but reversible infertility. Other drugs, including marijuana derivatives, phencyclidine, and alcohol, are believed to inhibit testosterone synthesis.