UK Yellow Card Reporting for GLP-1-Based Therapies Using Partial NHS Primary Care Prescribing and Hospital Medicine Data from England

Background/Objectives: In this retrospective aggregate pharmacovigilance study, we described UK Yellow Card reporting relative to partial English National Health Service (NHS) general practice (GP) prescribing for six glucagon-like peptide-1 (GLP-1)-based therapies. Methods: Primary overall reaction ratios used matching complete calendar years within each medicine: 2022–2025 for five medicines and 2024–2025 for tirzepatide. UK reaction counts were divided by English NHS GP items; geographical and product-coverage differences remain. Separate medicine estimates used conditional exact Poisson intervals without pooling. Annual models allowed for overdispersion. Outcome-specific extracts with unmatched windows and the combined GP plus estimated hospital denominator were secondary analyses. Results: Under the incomplete English NHS GP denominator, primary reaction ratios per million items were tirzepatide 23,808.48, semaglutide 5720.42, liraglutide 1700.45, exenatide 370.52, dulaglutide 258.11, and lixisenatide 87.70. Overall and severity report-based ratios were available for four medicines over their eligible periods. Temporal estimates were imprecise; tirzepatide had only two complete years, and lixisenatide had three reaction entries in its complete-year series, so neither received trend inference. Conclusions: Calendar matching improves the temporal definition of the overall ratios. Omitted private prescribing, UK–England population differences, uncertain product matching and reporting behaviour still prevent interpretation as incidence or comparative safety.