Objective: Analysis of arterial hypertension therapy for detection of drug interactions in routine ambulatory practice. Design and method: 402 case records of ambulatory hypertensive patients with comorbidity were analyzed. Evaluation of drug combinations from 27 agents with well-known metabolism each of them were conducted. Results: The mean number medications using by one comorbidity patient are 9,5 (from 5 to 14). The total number of used drugs are 95 (42 international nonproprietary names). Twenty two drug combinations (5,53%) were subsumed to major category. This category means the clinical significant drug interaction, and risk of drug adverse event exceeds them benefits. Most of major drug combinations were: simvastatine + amlodipine (0,73% among total medications, 13,2% among major combinations), simvastatine + itraconazole (0,44% and 8,09%, respectively), spironolactone + perindopril (0,57% and 10,34%, respectively). Besides that, combinations with amiodarone, spironolactone, simvastatin, amlodipine, diltiazem and clopidogrel are major drug combinations in 28,3%, 27,3%, 15%, 13%, 12,5% and 9% cases among total medical combinations. Twenty four drug combinations (5,73%) were subsumed to moderate category. This category means the moderate risk of drug adverse event development. Most of moderate drug combinations were: omeprazole + simvastatin (0,6% among total medications, 11,5% among moderate combinations), enalapril + medazolam (0,47% and 9,1%, respectively), fluvoxamine + losartan (0,44% and 8,5%, respectively). Fourteen percents of drug combinations with enalapril were subsumed to moderate category. Drug combinations with nifedipine, amiodarone and fluvoxamine were detected as moderate in 36%, 15,9% and 47,1% cases of total medical combinations. Conclusions: Drug administration for treatment of comorbidity patients in routine ambulatory practice usually performs without evaluation of possible drug interactions caused by changes of activity cytochrome P450 isozymes. About 11% of drug combinations which prescribes to ambulatory comorbidity patients are potential dangerous. In order to prevention of drug adverse event development in comorbidity patients is strongly effort to avoid combinations of drugs which have major or moderate profile.