Background and Objective: Medicinal drug interactions are one of the problems caused by irrational drug prescription. It eigher change the therapeutic effect or cause drug toxicity. This study was performed to determine the prevalence of medicinal drug interactions in medicinal prescriptions in Golestan province, north of Iran.

Methods: In this descriptive study, 1100000 medicinal prescriptions under contract with the Golestan province health insurance organization were assessed for drug interactions during 20 March-
20 September 2012.

Results: Drug interactions frequency was 6262 (0.66%). 35.5%, 63.1% and 1.4% of prescriptions were severe, moderate and mild interactions, respectively. The most common severe, moderate and mild drug interactions related to Atorvastatin-Gemfibrozil (13.67%), Ceftriaxone- Gentamicin (9.05%) and Lithium Carbonate-Haloperidol (2.56%).

Conclusion: In view of moderate and severe medicinal drug interactions in physicians' prescriptions, health system should plan a comprehensive program to improve awareness and effective monitoring to reduce medicinal drug interactions.