Reproductive toxicity and teratology evaluations of naltrexone

Reproductive toxicology and teratology studies of naltrexone are reviewed. Naltrexone produced behavioral changes in rats at doses below those which affected body weight. Excitatory signs and increased production of seminal plugs occurred in male rats. Prolonged administration to female rats resulted in excitatory signs and impaired maternal activity. Estrus cycling and fertility were decreased in female rats at doses that depressed body weight gain. Higher doses given to pregnant rats for shorter periods of time did not impair fertility or produce embryo or fetal toxicity. In rabbits, there was no evidence of behavioral changes. The highest dosage administered produced transient weight depression and possibly increased resorption. These data are consistent with a report of transient changes in some normal men given single doses of naltrexone. These effects may be mediated via hypothalamic and pituitary mechanisms involved in the control of luteinizing hormone levels.