OBJECTIVES: Many patients with serious mental illness (SMI) also have multiple comorbidities that require numerous medications. We measured how patients with SMI varied in their patterns of adherence to atypical antipsychotics, and how this variation predicted adherence patterns to other concurrent medications, including other SMI, anti-diabetes, or anti-hypertension oral medications.

METHODS: Our sample included patients from Truven Health claims databases with diagnoses of bipolar disorder, major depressive disorder, or schizophrenia. Patients were required to be prescribed an atypical antipsychotic as well as another oral medication to treat SMI (SSRI), type 2 diabetes (biguanides), or hypertension (ACE inhibitor) at the start of 2014. We defined a patient as adherent to a medication in a given month if the proportion of days covered ≥80%. Patient adherence patterns were modeled using a joint group-based trajectory model with a third-order polynomial. The predictive accuracy of atypical antipsychotic adherence—the share of patients who displayed the same pattern for their atypical antipsychotic and their other medication—was evaluated, and a t-test was conducted to compare predictive accuracy to random chance.

RESULTS: The 436,591 patients in our sample fell into four atypical adherence groups: a non-adherent group that discontinued after one to two months of treatment; a gradual discontinuation group; a group that stopped treatment after a few months but later restarted; and a group that was largely adherent for the full twelve months. Predictive accuracy of atypical antipsychotic adherence patterns across these trajectory groups was 49.6% for SSRIs, 44.5% for biguanides, and 44.5% for ACE inhibitors. These figures were 24.6%, 19.5%, and 19.5%, respectively, higher than random chance (all p < 0.001).

CONCLUSIONS: Patterns of adherence to atypical antipsychotics appear to predict similar patterns of adherence to other medications. Better measures of atypical antipsychotic adherence could thus improve the treatment of other conditions.