Experience with alcohol and the endogenous opioid system in ethanol analgesia.

This study employed naloxone, an opiate antagonist, to explore whether a learned opioid response, mediated by drinking experience, accounts for ethanol and placebo analgesia. Cold pressor pain was evaluated before and after ethanol (0.5 g/kg), placebo, and no-alcohol control treatments (administered in randomized order) and again after double-blind administration (6 mg/kg) of naloxone to 11 men and saline to 9. A triple interaction of treatments, antagonist conditions, and drinking experience indicated that naloxone as compared to saline diminished ethanol and placebo analgesia among experienced drinkers but had opposite effects among the same men in the control treatment. Six men, who reported that the injection of naloxone had an effect on pain, had higher drinking experience scores than the five men who reported naloxone had no effect. The similar pattern of response to both the alcohol and the placebo treatments suggests that the opioid system response to alcohol is learned.