In humans, 6-beta-naltrexol is the major metabolite of naltrexone, and its effectiveness at suppressing alcohol consumption in any species has not been previously investigated. Naltrexone is an opiate antagonist that reduces excessive drinking in many species, including humans with alcohol dependence. Whether 6-beta-naltrexol is an active metabolite that contributes to the efficacy of naltrexone remains unknown.Placebo and four doses of 6-beta-naltrexol were given by intraperitoneal injection to outbred Wistar rats and alcohol consumption was measured using a limited access model.6-beta-Naltrexol reduced alcohol consumption in a dose-dependent manner. At doses 7.5, 12.5, and 25 mg/kg, 6-beta-naltrexol significantly decreased consumption of a 6% ethanol solution compared with saline control groups.These data suggest that there may be a potential clinical use for 6-beta-naltrexol in recovering alcoholics.