The FDA Adverse Event Reporting System (FAERS) is the US pharmacovigilance database used by the FDA to detect safety signals in drug and biological product post-market surveillance. Healthcare providers, patients, and manufacturers submit adverse-event reports; the FDA maintains the database and reviews it for signals warranting further investigation.
On this site, FAERS appears primarily through the ongoing GLP-1 receptor agonist safety signal work. Compounded GLP-1 formulations have accumulated substantial FAERS report volume: 990 adverse events linked to compounded semaglutide and over 730 for compounded tirzepatide as of the July 2026 FDA safety statement. Many reports involve dosing errors, contamination, and formulation-related reactions distinct from the safety profile of the FDA-approved Wegovy, Ozempic, Zepbound, and Mounjaro products. FAERS data has been the primary evidence base cited by the FDA in its April 30, 2026 proposed rule to permanently exclude semaglutide, tirzepatide, and liraglutide from the Section 503B Bulks List (comment period closed July 30, 2026).
FAERS is also central to the emerging class-wide GLP-1 safety signal work on non-arteritic anterior ischaemic optic neuropathy (NAION), which the UK MHRA acted on in February 2026 and Australia's TGA acted on in July 2026. The FAERS reports formed part of the observational evidence base that supported those regulator actions, alongside published case-control and cohort studies from insurance claims and national registries. FAERS is a passive surveillance system with known limitations (voluntary reporting, causality assessment challenges, denominator uncertainty); regulators use it to detect signals but require confirmatory evidence for label changes. Stories here cover FAERS-driven regulatory actions and the pharmacovigilance chain from signal detection to label update. See [[pharmacovigilance]], [[naion]], and [[peptide-compounding]] for adjacent threads.
The FDA public comment period on the April 30, 2026 proposed rule to permanently exclude semaglutide, tirzepatide, and liraglutide from the Section 503B Bulks List closed Thursday July 30, 2026 after a Federal Register-extended deadline from the original June 29 cutoff. The FDA's underlying finding: no clinical need for FDA-registered outsourcing facilities to compound the three GLP-1 molecules from bulk drug substances. Section 503B outsourcing facilities are the FDA-registered large-scale compounding manufacturers (as distinct from state-licensed 503A pharmacies that compound for individual patient prescriptions). Finalization of the proposed rule would close the last legal pathway for large-scale FDA-registered 503B outsourcing facility compounding of the branded GLP-1 molecules, following the December 2024 semaglutide shortage resolution and February 2025 tirzepatide shortage resolution that ended the shortage-based compounding pathway. FDA rulemaking to finalize the exclusion after comment-period close typically takes 3-9 months depending on the volume and substance of received comments. Telehealth platforms including Hims & Hers Health (NYSE: HIMS) and LifeMD have already migrated to branded supply through Novo Nordisk and Eli Lilly commercial channels ahead of the expected 503B closure. FDA Adverse Event Reporting System (FAERS) data as of the July 2026 safety statement: 990 adverse events linked to compounded semaglutide, over 730 for compounded tirzepatide.
A 2026 chemistry study documented that when tirzepatide is compounded with vitamin B12 (a common differentiating additive used by compounding pharmacies to distinguish compounded products from the FDA-approved Mounjaro and Zepbound Eli Lilly formulations), the two substances can chemically bond and form a new molecule not present in the FDA-approved drug product. The finding adds to the accumulating pharmacovigilance case against compounded GLP-1 formulations, which are marketed as bioequivalent to the branded products but frequently contain non-FDA-approved additives whose long-term safety, immunogenicity, and pharmacokinetic profiles have not been characterized in registered clinical trials. Compounding-pharmacy additives often introduce impurities and reaction products that differ from the branded label chemistry. The chemistry-specific finding on tirzepatide + B12 bonding is the type of documented novel-molecule outcome that FDA safety scientists cited in the underlying rationale for the April 30, 2026 proposed rule to exclude semaglutide, tirzepatide, and liraglutide from the Section 503B Bulks List. FDA Adverse Event Reporting System (FAERS) data as of July 2026: 990 adverse events linked to compounded semaglutide, over 730 for compounded tirzepatide. The FDA 503B comment period on the exclusion closed Thursday July 30, 2026.
An FDA Adverse Event Reporting System (FAERS) entry logged April 30 surfaced publicly May 4, documenting hepatic failure in a 56-year-old male patient on Foundayo (orforglipron). The case was marked for expedited review and could have occurred at or before April 15 — Foundayo only launched April 9. There have been 34 total Foundayo FAERS reports so far, with two considered serious. LLY traded down nearly 3% premarket — hitting roughly $936 — before recovering on Lilly's response. Foundayo's label carries a warning that the medication is 'not recommended for use in patients with severe hepatic impairment' (orforglipron is primarily hepatically metabolized), but mild and moderate liver impairment is allowed at standard dose.
Analysis of the FAERS database (2012–2025) examining exenatide, liraglutide, dulaglutide, semaglutide, and tirzepatide reveals distinct risk profiles, suggesting not all GLP-1 agents carry the same safety concerns.