OBJECTIVES: This research aims to have a trial calculation on the medical cost reduction for the patient group prescribed the combination drug of ARB and calcium antagonist (a Combination Drug Group) against the patient group prescribed the combination use of ARB and calcium antagonist (a Combined Application Group). METHODS: We used the data of Japan Medical Data Center (JMDC), which provides health insurance claims data with linked health check-up data of 1.7 million members from health insurance societies in Japan. Since the data is not based on randomized controlled trial, we adjusted confounding factors using propensity score analysis. Through the examination, we found that the propensity score can be modeled by logistic regression including following four variables: age, square of age, log of medical cost before index time and square of log of medical cost before index time. RESULTS: As a result of our research, we estimated the adjusted average of medical cost for Combination Drug Group is lower by 900 yen per a month than that for Combined Application Group, which represents 1.7% of adjusted average monthly medical cost for Combined Application Group, 52,100 yen. CONCLUSIONS: Our research utilizing the real world data concluded that the combination drug of ARB and calcium antagonist can have a reductive, though limited, impact on the medical cost. Considering the general tendency that the medication cost itself of combination drug is higher than that of the combined use of drugs, we conclude that the result shows meaningful example of real world data analysis.