OBJECTIVES: To compare adherence to oral anti-diabetic (OAD) medications in users and non-users of antipsychotic medications. Among antipsychotic users, adherence to OADs and antipsychotics was compared. METHODS: This was a retrospective database analysis using Texas Medicaid prescription claims data. Adult patients (18-64 years) newly initiated on OADs were identified and followed for one-year. Medication adherence to OADs was evaluated in all patients, and adherence to antipsychotics was measured in the antipsychotic user cohort. Proportion of Days Covered (PDC) was used as the medication adherence measurement, with optimal adherence defined as PDC ≥ 0.8. Bivariate and multivariate analyses were used to compare adherence between treatment groups.    RESULTS: A total of 18,999 patients met the study inclusion criteria of which 1,956 (10.30%) were prescribed antipsychotics during the study period. The overall mean (SD) PDC was 0.57 (0.28) for the OADs, and 0.78 (0.25) for antipsychotics. The mean PDC for OADs was significantly higher for antipsychotic users compared to non-users (0.62 vs. 0.57; p<0.0001).  About 37% of antipsychotic users and 27% of non-users were adherent to OADs (p<0.0001). After controlling for age, gender, and pre-index chronic disease score, patients prescribed antipsychotics were 1.6 times more likely to be adherent compared to non-users (p<0.0001). In the subgroup of patients prescribed both medication types, higher PDC values were associated with antipsychotic drugs than with OADs (0.78 [0.25] vs 0.62 [0.29], p<0.05).  CONCLUSIONS: OAD medication adherence was better among antipsychotic users compared to non-users in the Texas Medicaid population.  However, overall adherence to OADs and antipsychotics was suboptimal in this population. The low adherence rates highlight need for interventions to help improve medication management for patients.