The U.S. Pharmacopeia released reference standards and analytical reference materials to help manufacturers and labs ensure purity and detect impurities in GLP‑1 peptide therapeutics amid surging demand and counterfeit products. USP emphasized the technical complexity of peptide characterization and the need for standardized materials to validate analytical methods. At the same time, clinicians and researchers report substantial interindividual variability in weight‑loss response to GLP‑1 receptor agonists such as semaglutide, with real‑world nonresponder rates up to roughly one in four. Investigators are probing genetic, metabolic and microbiome factors that may explain differential outcomes. Regulators including the FDA and EMA have warned about fraudulent GLP‑1 injections and product quality issues; USP’s materials aim to strengthen supply‑chain testing and reduce patient risk during a period of rapid market expansion.