Regulatory Interventions for Package Inserts and Patient Medication Information: A Systematic Review

Background/Objectives: Package inserts and patient medication information aim to translate complex evidence into practical instructions for safer use. Regulators have standardized content, format, user testing, risk wording, and distribution, but effects along the pathway from readability to medication safety remain unclear. Methods: We searched PubMed/MEDLINE, Embase, Web of Science, Scopus, regulator websites, and citations up to 23 July 2026. Eligible reports evaluated a mandated or endorsed requirement, template, wording, testing process, distribution program, or named initiative. Two reviewers independently screened, assessed full texts, extracted data, and judged methodological quality, resolving disagreements by consensus. Results: Of 2817 records, 34 full texts were assessed, 6 excluded, and 28 reports (27 studies) included. Due to heterogeneity, we synthesized descriptively using an intervention–outcome framework. Standardized structure, user-centered redesign, numerical risk formats, and performance-based testing were generally associated with better information finding and comprehension. Verbal descriptors like “common” or “rare” produced higher perceived probabilities than numerical formats. Large US studies of Medication Guides and consumer information documented excessive length, high reading levels, incomplete objective comprehension, inconsistent distribution quality, and limited risk knowledge. Overall test performance sometimes masked failures in emergency sequencing, contraindications, or applicability. Evidence for adherence, errors, adverse events, and healthcare utilization remained sparse. Conclusions: The findings support prioritized core structure, plain language, numerical risk communication, target-user testing, delivery verification, accessible formats, and post-implementation monitoring. Benefits are best established for proximal communication outcomes; effects on real-world safety remain uncertain.