Orlistat-Associated Gastrointestinal, Hepatobiliary, Pancreatic, and Anorectal Safety Signals: A FAERS Disproportionality and Regulatory Label Concordance Study.

Background/Objectives: Orlistat is a gastrointestinal lipase inhibitor used for weight management. Although its established safety profile is largely characterised by fat malabsorption-related gastrointestinal events, post-marketing reports suggest a broader spectrum of adverse events. Given the increasing intersection between obesity pharmacotherapy and the management of non-alcoholic fatty liver disease/metabolic dysfunction-associated steatotic liver disease (NAFLD/MASLD), this study evaluated gastrointestinal, hepatobiliary, pancreatic, and anorectal adverse-event reporting signals associated with orlistat in the U.S. Food and Drug Administration (FDA) Adverse Event Reporting System (FAERS) and assessed concordance with regulatory prescribing information. Methods: Quarterly FAERS files from 2004 Q1 through 2026 Q1 were analysed; some retained reports had Initial FDA Received Date (FDA_DT) values dating back to 1999. Descriptive analyses included all orlistat-associated reports, whereas disproportionality analyses were restricted to primary-suspect reports. Sixty-five prespecified Medical Dictionary for Regulatory Activities (MedDRA) preferred terms (PTs) were screened. Reporting odds ratios (RORs), 95% confidence intervals (CIs), and proportional reporting ratios (PRRs) were calculated. A signal was defined as ROR > 2.0, lower bound of the 95% CI > 1.0, and n ≥ 3. Two-sided p values calculated using Fisher's exact test on the corresponding 2 × 2 contingency tables were adjusted using the Benjamini-Hochberg false discovery rate procedure to address multiple testing. Signal-positive PTs were cross-referenced with prescribing information from three jurisdictions. Results: Overall, 30,454 deduplicated orlistat-associated reports were identified, including 16,684 primary-suspect reports. Thirty-eight of the 65 prespecified MedDRA PTs met the signal criteria, and all remained statistically significant after Benjamini-Hochberg false discovery rate correction (q < 0.05). The strongest signals were rectal discharge (ROR 1175.53; 95% CI 1093.44-1263.78) and steatorrhoea (ROR 1147.99; 95% CI 1058.12-1245.50); change in bowel habit also showed a high ROR (47.32; 95% CI 38.27-58.51). Unlabelled signal-positive PTs included constipation, faeces hard, cholecystitis, and irritable bowel syndrome; change in bowel habit showed jurisdiction-specific labelling discordance. Conclusions: Orlistat-associated FAERS signals included both expected fat-malabsorption-related events and additional gastrointestinal, hepatobiliary, pancreatic, and anorectal PTs, several of which were not explicitly represented in the evaluated regulatory labels. These findings reflect disproportionate reporting rather than incidence, absolute risk, or causality and require confirmation in independent clinical or epidemiological data sources. They do not, by themselves, support regulatory labelling changes.