In case of patients with alcohol addiction haloperidol is used to control the exacerbation of the addiction, but the empirical dose selection of haloperidol often results in adverse side effects. Microsomal isozyme cytochrome P450 3A4, the activity of which has wide variability, takes part in biotransformation of haloperidol. The study involved 35 men with alcohol addiction. The efficacy and safety of haloperidol was evaluated by international psychometric scales. The activity of CYP3A4 was evaluated by determination endogenous substrate of this isoenzyme and its metabolite in urine - (the ratio of 6-beta-hydrocortizol/corizol). The study revealed a statistically significant patterns between the activity of CYP3A4 and the efficacy and safety of haloperidol.