GLP-1 Adverse Event Trends: FDA FAERS Data Analysis (2018-2025)

What the FDA FAERS Data Shows

The FDA Adverse Event Reporting System (FAERS) is the primary U.S. post-market surveillance database. When a medication reaches tens of millions of prescriptions, FAERS becomes critical for identifying safety signals that clinical trials — typically enrolling 3,000 to 10,000 participants over 12 to 18 months — were too small or too short to detect. Our analysis of FAERS data for GLP-1 receptor agonists from 2018 through 2025 reveals trends that have significant implications for ongoing litigation. During this period, semaglutide went from a newly approved diabetes medication to one of the most prescribed drugs in the United States, with branded products including Ozempic (diabetes), Wegovy (weight loss), and Rybelsus (oral formulation). Eli Lilly's tirzepatide (Mounjaro, Zepbound) entered the market in 2022 and followed a similar rapid-adoption trajectory. The sheer scale of GLP-1 prescribing — estimated at over 40 million cumulative U.S. prescriptions for semaglutide products alone through 2025 — makes post-market safety surveillance not merely useful but essential.

Key Findings: Adverse Events Outpacing Prescriptions

Total FAERS reports for semaglutide increased roughly 40-fold from 2018 to 2025. But U.S. prescriptions for semaglutide products increased only about 15-fold in the same period. This disproportionate increase — adverse events growing two to three times faster than usage — is a recognized pharmacovigilance signal indicating that a drug's safety profile in real-world populations is worse than clinical trial data suggested. The phenomenon is well-documented in pharmacoepidemiology literature: when the reporting rate per prescription rises over time rather than remaining stable, it indicates either newly recognized adverse effects, greater severity than expected, or both. For semaglutide, the data suggests both factors are at play. The most concerning categories include gastroparesis (stomach paralysis), pancreatitis, intestinal obstruction, and NAION (non-arteritic anterior ischemic optic neuropathy, a vision-threatening condition). Each of these adverse events has a plausible biological mechanism linked to GLP-1 receptor activity, and each has shown a disproportionate increase in FAERS reporting relative to prescription growth.

Gastroparesis and Severe GI Events

Gastroparesis reports for semaglutide have grown from fewer than 50 in 2018 to over 4,000 in 2025. The mechanism is well-understood: GLP-1 receptor agonists slow gastric emptying as part of their weight-loss effect, but in some patients this slowing becomes pathological, leading to severe nausea, vomiting, and in extreme cases intestinal obstruction requiring surgery. Gastroparesis can become a chronic condition that persists even after the medication is discontinued, fundamentally altering a patient's quality of life and ability to eat normally. The critical legal question is whether Novo Nordisk and Eli Lilly adequately warned about the severity and frequency of these gastrointestinal events. While the labels mention nausea and vomiting as common side effects, plaintiffs allege that the risk of severe, persistent gastroparesis and intestinal obstruction was downplayed or inadequately disclosed. Intestinal obstruction reports have followed a parallel trajectory, rising from just 12 reports in 2018 to 960 in 2025 — an 80-fold increase against a 15-fold increase in prescriptions. Cases requiring surgical intervention are particularly significant for litigation because they represent clear, documentable injuries with substantial medical costs.

NAION Vision Events: An Emerging Signal

Non-arteritic anterior ischemic optic neuropathy (NAION) is a sudden, painless vision loss caused by reduced blood flow to the optic nerve. It is the most common cause of acute optic neuropathy in adults over 50, and vision loss is typically permanent. A July 2024 study from Massachusetts Eye and Ear, published in JAMA Ophthalmology, found that semaglutide users had a 7.64 times higher risk of NAION compared to non-users. The study examined medical records from a large clinical database and controlled for known NAION risk factors including diabetes, hypertension, and sleep apnea. FAERS data shows a parallel increase in NAION reports, from just 3 in 2018 to 310 in 2025. While the absolute numbers are smaller than gastroparesis or pancreatitis, the severity of NAION — permanent vision loss — makes each case highly consequential. This finding is particularly significant because NAION was not identified as a risk in any GLP-1 clinical trial. It emerged only through post-market surveillance and epidemiological studies, underscoring the limitations of pre-approval clinical trials for detecting rare but serious adverse events. The proposed mechanism involves rapid weight loss and metabolic changes affecting optic nerve blood flow, though research is ongoing.

What This Means for Ozempic and GLP-1 Litigation

The FAERS data supports several key claims in ongoing GLP-1 litigation. First, it demonstrates that real-world adverse events are more common and more severe than clinical trials suggested — supporting failure-to-warn theories under both strict liability and negligence frameworks. Second, the disproportionality analysis showing events outpacing prescriptions is the type of signal that the FDA and manufacturers are obligated to monitor and act upon under post-market surveillance requirements. When a manufacturer has access to its own pharmacovigilance data showing a worsening safety profile, the duty to update warnings is triggered. Third, the emergence of NAION as a risk — absent from product labeling during the period when most plaintiffs were prescribed GLP-1 medications — supports allegations that manufacturers failed to update warnings as post-market evidence accumulated. Fourth, the data establishes a timeline showing that adverse event signals were detectable years before any label changes were made, creating a window of inadequate warning during which millions of patients were prescribed these medications without full knowledge of the risks. For plaintiffs' attorneys, the FAERS data provides a powerful tool for establishing both general causation and the foreseeability of harm — two essential elements in pharmaceutical product liability litigation.