A patient perspective of the impact of medication side effects on adherence: results of a cross-sectional nationwide survey of patients with schizophrenia

Background: Antipsychotic medications often have a variety of side effects, however, it is not well understood how the presence of specific side effects correlate with adherence in a real-world setting. The aim of the current study was to examine the relationship between these variables among community-dwelling patients with schizophrenia. Methods: Data were analyzed from a 2007-2008 nationwide survey of adults who self-reported a diagnosis of schizophrenia and were currently using an antipsychotic medication (N = 876). The presence of side effects was defined as those in which the patient reported they were at least "somewhat bothered". Adherence was defined as a score of zero on the Morisky Medication Adherence Scale. To assess the relationship between side effects and adherence, individual logistic regression models were fitted for each side effect controlling for patient characteristics. A single logistic regression model assessed the relationship between side effect clusters and adherence. The relationships between adherence and health resource use were also examined. Results: A majority of patients reported experiencing at least one side effect due to their medication (86.19%). Only 42.5% reported complete adherence. Most side effects were associated with a significantly reduced likelihood of adherence. When grouped as side effect clusters in a single model, extra pyramidal symptoms (EPS)/agitation (odds ratio (OR) = 0.57, p = 0.0007), sedation/cognition (OR = 0.70, p = 0.033), prolactin/endocrine (OR = 0.69, p = 0.0342), and metabolic side effects (OR = 0.64, p = 0.0079) were all significantly related with lower rates of adherence. Those who reported complete adherence to their medication were significantly less likely to report a hospitalization for a mental health reason (OR = 0.51, p = 0.0006), a hospitalization for a non-mental health reason (OR = 0.43, p = 0.0002), and an emergency room (ER) visit for a mental health reason (OR = 0.60, p = 0.008). Conclusions: Among patients with schizophrenia, medication side effects are highly prevalent and significantly associated with medication nonadherence. Nonadherence is significantly associated with increased healthcare resource use. Prevention, identification, and effective management of medication-induced side effects are important to maximize adherence and reduce health resource use in schizophrenia.