The use of the theory of planned behavior to predict medication adherence in schizophrenia

Objective: Inadequate adherence to antipsychotic medication regimens is common among patients with schizophrenia. This study evaluated the psychometric properties of a new instrument designed to identify the factors associated with poor adherence to antipsychotic medications in this population. Methods: Spanish-speaking, Mexican-American adult patients with schizophrenia (N=155) were administered the newly developed Theory of Planned Behavior (TPB) Inventory, as well as the Rating of Medication Influences (ROMI) scale and the Treatment Compliance Interview (TCI). The latter two instruments are commonly used and well validated for the assessment of medication adherence among patients with schizophrenia. Results: The TPB Inventory demonstrated high internal consistency, excellent test-retest reliability and good concurrent validity with the ROMI. In addition, the TPB Inventory showed good predictive validity with patients' intentions to take medication as prescribed and actual adherence behavior. Conclusions: The TPB Inventory is a reliable and valid instrument that can be used to assess the factors associated with medication nonadherence. Better understanding of these factors can guide clinicians in their efforts to improve medication adherence among patients with schizophrenia.