According to literature data, isoenzyme CYP3A4 of cytochrome P450 is involved in biotransformation of drugs.,At the same time, there is evidence that carbamazepine induces CYP3A4 activity. The purpose of the study was to evaluate the effect of carbamazepine on the CYP3A4 activity in patients with alcohol addiction. The study was performed on a group of 25 men with alcohol abuse, which received haloperidol during the exacerbation of addiction. The activity of CYP23A4 was evaluated using high performance liquid chromatography with mass spectrometry (HPLC-MS/MS) for determining 6-beta-hydroxycortisol conversion to cortisol in urine. The results were used to construct a plot and derive an equation of logarithmic regression reflecting the dependence of CYP3A4 activity on the dose of carbamazepine: y = (5.5 - 9.1) x 10⁻⁵ - ΔΔx². These data demonstrate a statistically significant effect of carbamazepine on the activity of CYP3A4 isoenzyme in patients with alcohol addiction treated by haloperidol.