Intentional non-adherence to antipsychotic medication in patients with schizophrenia

Background: Although adherence to antipsychotic medication is critical in the treatment of schizophrenia, prior studies have not adequately distinguished between intentional and unintentional non-adherence.

Methods: This study included outpatients with schizophrenia. Self-reported intentional non-adherence was assessed cross-sectionally using the Japanese version of the Intentional Non-Adherence Scale (INAS-J). Item G12 of the Positive and Negative Syndrome Scale (PANSS), Medication Possession Ratio (MPR), psychiatric symptoms, side effects, and medication status were also assessed. An exploratory factor analysis was carried out to examine the factor structure of the INAS. Multiple regression analyses were conducted to examine factors associated with intentional non-adherence.

Results: A total of 93 patients were included. The mean ± SD of INAS total score was 36.6 ± 16.2 (out of a maximum score of 110), with 33 subjects (35.5 %) having a minimum score of 22. The mean MPR was 98.2 ± 10.0 %, and the mean score for PANSS G12 was 1.8 ± 1.1. These suggested that they had well-preserved illness insight and good medication adherence. Exploratory factor analysis of the INAS revealed two factors, "Concern about medication" and "Confirming medication need". No variables were significantly associated with the INAS total score.

Conclusions: This is the first study to evaluate intentional non-adherence in patients with schizophrenia. Intentional non-adherence was low in this population. Our findings should be interpreted in the context of patients presenting with relatively well-preserved insight and good medication adherence. Further investigations using the INAS are warranted to examine intentional non-adherence in patients with more diverse backgrounds.