Medication adherence measurement methods and their reported relationship with medication safety outcomes: a scoping review

OBJECTIVE: To map medication adherence measurement methods used in studies examining medication safety outcomes in adults receiving long-term pharmacotherapy, and to describe how adherence-safety relationships have been studied and reported. METHODS: A scoping review was conducted using systematic searches of PubMed, Web of Science, and Scopus from 1 January 2000 to 9 February 2026. Eligible studies were those that explicitly examined the relationship between adherence and at least one medication safety outcome. RESULTS: = 1, 3.4%) were also identified. Analytical direction varied: 15 studies examined safety-to-adherence pathways, where medication safety burden or safety-related factors were treated as the exposure or predictor of adherence, non-adherence, or discontinuation; six examined adherence-to-safety pathways, where adherence, non-adherence, persistence, or adherence trajectory was treated as the exposure or predictor of subsequent medication safety outcomes; five were cross-sectional/descriptive/undirected; and three had complex or indirect analytical structures. CONCLUSION: This scoping review shows that adherence-safety relationships have been studied across heterogeneous diseases, measurement approaches, safety outcomes, and analytical directions. Most studies examined safety-to-adherence pathways, whereas fewer examined adherence-to-safety pathways, and many designs could not establish temporality. Findings suggest that adherence assessment, medication review, and adverse drug reaction monitoring may be more informative when considered together, particularly in pharmacy practice. Greater standardization of adherence constructs and safety outcome definitions, clearer reporting, longitudinal designs, and explicit conceptual models are needed to strengthen future research.