Methadone reduces sexual performances and sexual motivation in the male Syrian golden hamster.

The debilitating effect of opiate drugs on sexual function has been known clinically for hundreds of years but has become a topic of experimental investigation only recently. The purpose of the current study was to examine the effects of the opiate drugs methadone and the opiate blocking drug naltrexone on the sexual behavior of male hamsters. Methadone, administered at dosages of 1, 2, 4, 8, and 16 mg/kg, was found to cause a dose related decline in measures of both sexual performance and sexual motivation, with measures of sexual performance being the more sensitive to the drug. The debilitating effect of methadone was judged to be highly selective for sexual behavior since, for example, at 16 mg/kg of methadone, sexual behavior was eliminated but ambulatory activity was unaffected. Pretreatment with naltrexone blocked the effects of methadone and posttreatment reversed the effects, thereby indicating that the methadone was inhibiting sexual behavior by acting on specific opiate receptors. The results demonstrate that the male hamster is an excellent small animal model for use in studying the mechanisms of opiate induced sexual dysfunction and further support the hypothesis that the endogenous opiates may be involved in the regulation of sexual behavior.