Opioids and intake of alcoholic beverages

Rats were given a daily opportunity to consume a sweetened ethanol solution (ES) or water until they took about 2.0 g/kg of pure ethanol (E) during 1.5 hr/day. Then, rats were given one of a number of opioids before an opportunity to drink. Some opioids, e.g., morphine (MOR), methadone, and fentanyl, at small doses, increase ES-intake; some decrease intakes, e.g., naloxone (NX) and MR 2266. Diprenorphine, a mixed agonist-antagonist having no analgesic potential and blocking other opioids' analgesia, increases ES-intake across a wide range of doses beginning with 0.003 mg/kg.