A systematic review of factors influencing adherence to antipsychotic medication in schizophrenia-spectrum disorders

• We conducted a systematic review of medication adherence factors in schizophrenia.
• Positive attitude to medication and illness insight appear to impact adherence.
• Contradictory results were found for all other factors examined in our sample.
• Prospective studies with longer durations and larger samples are urgently needed.

Adherence to antipsychotics improves outcome in schizophrenia. There is a lack of consensus on which factors most influence adherence behaviour and methodological issues hinder interpretation of existing evidence. A rigorous systematic search designed to identify robustly implicated factors emerging from methodologically rigorous studies narrowed our search to 13 observational studies (total N=6235) relating to adherence, antipsychotics and schizophrenia. Studies varied significantly, with reported adherence rates ranging from 47.2% to 95%. Positive attitude to medication and illness insight were the only factors consistently associated with better adherence, while contradictory results were found for socio-demographic characteristics, symptom severity and side effects. Only distinct aspects of the therapeutic relationship and social support in younger patients were related to good adherence. Antipsychotic type or formulation and neurocognitive functioning did not appear to impact medication adherence. Despite greater methodological rigour in determining studies to include in the present systematic review, it remains difficult to guide clinicians in this vital area and most of the work discussed contained small sample sizes. Future research in this field should therefore prioritise prospective study designs over longer periods and larger samples in naturalistic settings, providing a more appropriate and clinically meaningful framework than widely used cross-sectional designs.