Several investigators have studied the drug-drug interaction that may exist when alcohol and H2-receptor antagonists (i.e. cimetidine, ranitidine, famotidine) are administered concomitantly. Results from these studies have been mixed. However, no systematic investigation of the change in blood alcohol concentrations in the social drinker versus the chronic drinker challenged by concurrent intake of alcohol and H2-receptor antagonist has been conducted.Eleven volunteers participated in this 14-day study. On day 0, study participants were administered an oral alcohol dose of 0.15 g/kg. On days 1 to 9, no medication was given. All volunteers then received cimetidine 400mg twice daily on days 10 to 13. On day 14, study participants received an oral alcohol dose of 0.15 g/kg after their morning dose of cimetidine. Blood sampling was performed on days 0 and 14 after alcohol administration.The comparative alcohol availabilities, pre- and post-cimetidine, were determined by comparing the time to peak plasma concentration (tmax), peak plasma concentration (Cmax), and the total area under the concentration-time curve (AUC). In the chronic drinkers, tmaxwas significantly shorter than in the social drinkers following cimetidine administration (p = 0.008).Chronic drinkers who drink after cimetidine administration will have higher concentrations of alcohol faster than social drinkers. Medicolegal consequences resulting from this drug-drug interaction may occur; clinicians should therefore counsel patients about the possibility of enhanced impairment resulting from concurrent administration of these 2 drugs.