Across the full spectrum of major clinical trials evaluating glucagon-like peptide-1 receptor agonists (GLP-1 RAs) for obesity management, nausea consistently emerges as the most documented adverse effect, yet the methods used to capture it have received little scrutiny relative to their clinical importance. This narrative review traces how nausea was actually measured across the pivotal liraglutide (SCALE), semaglutide (STEP) and tirzepatide (SURMOUNT) obesity trial programmes, and situates those methods against the standards set out in the Consensus-based Standards for the selection of health Measurement Instruments (COSMIN) and the United States Food and Drug Administration's Patient-Focused Drug Development guidance. Across all three drug classes, nausea was ascertained through investigator-recorded, spontaneously reported adverse events coded to the Medical Dictionary for Regulatory Activities (MedDRA), a pharmacovigilance framework built for a different purpose than symptom characterization, rather than through any validated, symptom-specific patient-reported outcome instrument. This observation gains further importance when considered alongside a second, less widely recognized fact: these same trial programmes devoted substantial methodological effort to developing and implementing a rigorous, quality of life measure specifically for obesity, the Impact of Weight on Quality of Life-Lite Clinical Trials Version in addition to the Short Form-36 and EuroQol-5D. We argue that this asymmetry, more than any single mismeasurement, helps explain why real-world persistence with these agents falls so far short of what trial-reported tolerability figures would predict, and we outline what a fit-for-purpose metabolic nausea instrument would need to capture that adverse-event surveillance cannot.
