Endogenous opioids and alcohol dependence: opioid alkaloids and the propensity to drink alcoholic beverages

Rats consume alcoholic beverages in a wide variety of circumstances. Opioid antagonists, naloxone and naltrexone, decrease intake of many ingesta, including alcoholic beverages. Small doses of morphine increase intake of alcoholic beverages. Further, the effects of small doses of morphine are persistent and there is no sign that tolerance to morphine's ability to increase alcohol intake develops as seen with morphine's ability to produce analgesia. Morphine's effects can combine with other variables that enhance intake of alcoholic beverages to produce very large daily intakes of ethanol. These generalizations, from a large number of separate experiments, support the conclusion that alcoholism is a special case of an ingestive disorder involving opioidergic systems.