Naltrexone persistently reduces rats' intake of a palatable alcoholic beverage.

Rats were given 30 days of opportunity to take a sweetened alcoholic beverage and water for 2 hr/day. At first, they took little alcohol, but subsequently took, on average, 2.3 g/kg of alcohol/daily session. They also took sufficient water, during the 2-hr period, to maintain their health and to steadily gain weight. At the end of the 30 days, they were divided into four groups so that their intakes of alcohol were similar. All groups continued on the daily regimen, but each group received different injections. One group received placebos, whereas the other two groups received either 5.0 or 10.0 mg/kg, respectively, of naltrexone daily, 30 min before the drinking session. The fourth group received 5.0 mg/kg of naltrexone 12.5 hr before the session and another 5.0 mg/kg 30 min before the session. This regimen of dosing and daily opportunities to drink continued for 30 days. With the end of injections, subjects continued on the regimen for another 5 days. Naltrexone, dose-relatedly, reduced rats' intake of alcoholic beverage. Furthermore, with respect to reducing intake of alcohol, no tolerance or refractoriness were observed across the 30 days of dosing. Within a couple of days after dosing, levels of intake returned to predosing levels.