Patients’ beliefs about medications are key barriers to and facilitators of medication adherence. Perceived risks of having a side effect and perceived impact and need for the medication were common themes throughout the literature, with 24 articles in our review covering one of these topics. In the 21 articles in which the relationship between beliefs about medications and adherence was clearly identified, 16 of those relationships were strongly positive in adjusted analysis. Only four articles used electronic monitoring to measure adherence; the majority used self-report. The specific beliefs discussed in each article are variable, and, in some articles, certain beliefs might be strongly associated with adherence, and others not. For example, Aikens and Piette interviewed 806 patients with diabetes and hypertension in several clinics in Flint, Michigan, using the well-validated Beliefs About Medication questionnaire.31 Concerns about the long-term effects of medication use were negatively associated with adherence to medication after controlling for costs and demographics, whereas beliefs about the necessity of the medication to maintain health were not associated with adherence. Beliefs about medications are complex but vital to understand in shaping interventions and policy solutions