Background: Poor adherence to oral antipsychotics is common in patients with schizophrenia; nonetheless, there has been no systematic review or meta-analysis on medication adherence measured by electronic adherence monitoring (EAM), considered by many as the ‘gold standard’ assessment. Methods: We systematically searched MEDLINE and Embase to identify studies investigating adherence to oral antipsychotics using EAM in patients with schizophrenia spectrum disorder. There were no exclusion criteria. We looked at the methodology in each study and defined which type of adherence was used in the study. Data on medication adherence, definition of satisfactory adherence (i.e., the threshold set in terms of the percentage of times medication was taken as prescribed), and factors associated with adherence were extracted for the included studies. Further, data on the rates of medication adherence were quantitatively synthesized. Results: A total of 19 studies involving 2184 patients were included. EAM-measured medication adherence was classified into three outcome types: taking adherence, regimen adherence, and timing adherence. The meta-analysis yielded oral antipsychotic adherence rates (defined as a continuous variable) of 71.1% for taking adherence [from seven studies, n = 256, 95% confidence interval (CI) 58.0–84.1], 70.0% for regimen adherence (from five studies, n = 174, 95% CI = 63.6–76.4), and 64.9% for timing adherence (from four studies, n = 212, 95% CI 53.2–76.6), respectively. The proportions of patients with oral antipsychotic adherence, when defined as a dichotomous variable, ranged from 50 to 78.3% for the 70% threshold for satisfactory adherence, 29.8–75.7% for the 75% threshold, and 47.8–75.7% for the 80% threshold. Factors associated with poor medication adherence were greater symptom severity, more frequent dosing regimen, poorer insight, and more negative drug attitude. Conclusions: Oral antipsychotic adherence rates in schizophrenia, defined as a continuous variable and measured by EAM, were in the range of 70%, lower than the 80% threshold used widely to define satisfactory adherence.
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