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OBJECTIVES The aim of this study was to examine the characteristics of patients, physicians, and medical facilities, and their association with prescriptions that do not include metformin as the initial oral antidiabetic agent. STUDY DESIGN Observational, cross-sectional study. METHODS Patients with incident type 2 diabetes between January 1, 2006, and December 31, 2010, were identified from the Taiwan National Insurance Research Database. We describe trends in the initial prescription of antidiabetic medications that do not contain metformin during the study period. A multivariable logistic model and a multilevel linear model were used in the analysis of factors at a range of levels (patient, physician, and medical facility), which may be associated with the selection of oral antidiabetic drugs. RESULTS During the study period, the proportion of prescriptions that did not include metformin declined from 43.8% to 26.2%. Male patients were more likely to obtain non-metformin prescriptions (adjusted odds ratio [OR]: 1.15; 95% confidence interval [CI]: 1.08-1.23), and the likelihood that a patient would be prescribed a non-metformin prescription increased with age. Physicians aged ≥35 years and those with specialties other than endocrinology tended to prescribe non-metformin prescriptions. Metformin was less commonly prescribed in for-profit hospitals (adjusted OR: 1.34, 95% CI: 1.11-1.61) and hospitals in smaller cities (adjusted OR: 1.28, 95% CI: 1.05-1.57) and rural areas (adjusted OR: 1.83, 95% CI: 1.32-2.54). CONCLUSIONS Disparities continue to exist in clinical practice with regard to the treatment of diabetes. These inequalities appear to be linked to a variety of factors related to patients, physicians, and medical facilities. Further study will be required to understand the effects of continuing medical education in enhancing adherence to clinical guidelines.