The ongoing monitoring of drug safety after approval—watching for rare or delayed side effects that clinical trials were too small or short to detect.Pharmacovigilance is the science and practice of detecting, assessing, understanding, and preventing adverse effects of pharmaceutical products throughout their lifecycle. Post-marketing surveillance (Phase IV) captures rare adverse events that pre-approval trials (typically thousands of patients, months to years of follow-up) cannot detect. For peptide therapeutics, pharmacovigilance is particularly important for identifying long-term effects of chronic receptor activation, immunogenicity (anti-drug antibody formation), and off-target effects at receptors with broad physiological roles.