GLP-1 Receptor Agonist Litigation: What Attorneys Need From Medical Experts
More than 3,800 federal lawsuits allege that GLP-1 receptor agonist medications, including Ozempic, Wegovy, Mounjaro, and Zepbound, caused severe gastrointestinal injuries that persisted long after patients stopped taking the drugs. With Rule 702 hearings scheduled for September 2026 and case filings still accelerating, the demand for qualified gastroenterology, endocrinology, and pharmacology expert witnesses is surging.
The Litigation Landscape
The GLP-1 receptor agonist mass tort has become one of the largest and fastest-growing pharmaceutical litigations in the country. As of the July 1, 2026 JPML statistics report, 3,848 cases are pending in MDL No. 3094 in the Eastern District of Pennsylvania, with 3,882 total historical actions filed.1
A separate MDL, No. 3163, consolidates 146 cases alleging vision loss (non-arteritic anterior ischemic optic neuropathy, or NAION) linked to GLP-1 medications. Both MDLs are before Judge Karen Spencer Marston.
Eight GLP-1 RA medications are at issue across two defendant manufacturers:2
- Novo Nordisk: Ozempic (semaglutide injection), Wegovy (semaglutide injection for weight loss), Rybelsus (oral semaglutide), Victoza (liraglutide), and Saxenda (liraglutide for weight loss)
- Eli Lilly: Mounjaro (tirzepatide), Zepbound (tirzepatide for weight loss), and Trulicity (dulaglutide)
Plaintiffs allege that both manufacturers failed to adequately warn consumers and prescribers about the risk of severe, persistent gastrointestinal injuries, particularly when these drugs were prescribed off-label for weight loss prior to formal FDA approval for that indication. The litigation has been gaining momentum steadily:
- February 2024: The JPML centralized GLP-1 GI injury cases into MDL 3094 in the Eastern District of Pennsylvania.
- January 2026: Case count surpassed 3,000 pending actions.
- May 2026: Rule 702 expert exclusion motions and summary judgment motions filed by both sides.
- September 2026: Rule 702 hearings scheduled for September 10 through 18, a pivotal moment that will determine which expert testimony survives for trial.
No global settlement or bellwether trial has been scheduled as of mid-2026. The litigation remains in its pretrial phase, but the Rule 702 hearings will be the first major test of the scientific evidence on both sides.
The Injuries at Issue
The core injuries alleged in MDL 3094 involve severe gastrointestinal conditions that plaintiffs say developed during or after GLP-1 medication use and, critically, did not resolve after discontinuation. The primary conditions include:
Gastroparesis (Stomach Paralysis)
Gastroparesis is a condition in which the stomach cannot empty food at a normal rate. Patients experience chronic nausea, vomiting, severe abdominal pain, bloating, and malnutrition. In its most severe forms, gastroparesis can require surgical intervention, feeding tubes, or gastric electrical stimulation. Plaintiffs allege that GLP-1 medications caused persistent gastroparesis that continued months or years after stopping the drug.
Bowel Obstruction and Ileus
Intestinal obstruction occurs when food or waste cannot move through the intestines. Ileus is a related condition in which the intestines stop contracting normally. Both can require emergency surgery, hospitalization, and carry a risk of bowel perforation, sepsis, and death.
Gallbladder Disease
Claims include cholecystitis (gallbladder inflammation), cholelithiasis (gallstones), and choledocholithiasis (bile duct stones). Many plaintiffs underwent cholecystectomy (gallbladder removal surgery) that they allege was a direct consequence of GLP-1 medication use.
Pancreatitis
Acute and chronic pancreatitis claims allege that GLP-1 medications triggered dangerous inflammation of the pancreas, sometimes requiring hospitalization, intensive care, and long-term dietary restrictions.
Vision Loss (NAION)
A separate track of litigation (MDL 3163, also before Judge Marston) involves claims that GLP-1 drugs caused non-arteritic anterior ischemic optic neuropathy, a sudden loss of blood flow to the optic nerve that can result in permanent vision impairment or blindness.
The Science Behind the Claims
The scientific foundation for this litigation draws from multiple lines of evidence connecting GLP-1 receptor agonism to gastrointestinal injury.
How GLP-1 Drugs Affect the Gut
GLP-1 receptor agonists work by mimicking glucagon-like peptide-1, a naturally occurring hormone that regulates blood sugar by stimulating insulin release, suppressing glucagon, and, critically, slowing gastric emptying. This delayed gastric emptying is not a side effect. It is a core pharmacological mechanism of the drug class. It reduces appetite and promotes weight loss by keeping food in the stomach longer.
The clinical question at the center of this litigation is whether that mechanism, at therapeutic doses and over prolonged use, can cause permanent or long-lasting damage to gastric motility.
Key Published Research
University of British Columbia / JAMA Study (2023): A large cohort study using the PharMetrics Plus database (a random sample of 16 million U.S. patients, 2006 to 2020) examined GLP-1 agonist users without diabetes who were taking the drugs for weight loss. Compared to bupropion-naltrexone (an unrelated weight loss medication), GLP-1 users had significantly increased hazard ratios for:3
- Biliary disease (including cholecystitis, cholelithiasis, and choledocholithiasis)
- Pancreatitis (including gallstone pancreatitis)
- Bowel obstruction
- Gastroparesis
This study is significant because it isolated GLP-1 users without diabetes, removing the confounding factor that diabetes itself increases GI risk. It demonstrated that the gastrointestinal risks persist even in the non-diabetic weight loss population, the exact population driving the current explosion in prescriptions.
FDA and Health Canada Label Updates (2024): In March 2024, the Ozempic product monograph was updated to warn that “use of GLP-1 receptor agonists may be associated with severe gastrointestinal disease” and that “events of delayed gastric emptying, dysgeusia and ileus have been reported.” In July 2024, Mounjaro and Trulicity labels were similarly updated to warn that “events related to impaired gastric emptying, including severe gastroparesis, have been reported.”4
Plaintiffs argue that these label changes came too late and that the manufacturers had evidence of these risks well before the labels were updated.
Clinical Review (2024): A published clinical review examined the consequences of delayed gastric emptying with GLP-1 RAs and tirzepatide, noting increased frequency of retained gastric contents at endoscopy, risks of pulmonary aspiration during anesthesia, and the clinical significance of the long half-lives of these drugs in periprocedural settings.5
Why Expert Witnesses Are Critical
With Rule 702 hearings set for September 10 through 18, 2026, both plaintiffs and defendants are assembling their expert witness teams for what will be the most consequential phase of this litigation to date. This MDL demands expertise across multiple medical specialties.
Gastroenterology Experts
Gastroenterologists are at the center of this litigation. They are needed to:
- Explain the mechanisms of gastroparesis, ileus, and bowel obstruction in the context of GLP-1 pharmacology
- Review plaintiffs’ medical records and establish whether their GI conditions were caused by the medication versus preexisting conditions
- Testify on the clinical presentation, diagnosis, and treatment of drug-induced gastroparesis
- Distinguish between transient delayed gastric emptying (an expected drug effect) and persistent gastroparesis (an alleged injury)
- Address the standard of care for monitoring patients on GLP-1 medications for GI complications
- Opine on whether the injuries resolve after drug discontinuation or represent permanent damage
Endocrinology Experts
Endocrinologists prescribed these medications and understand their clinical use, dosing protocols, and risk-benefit calculus. They may be asked to:
- Testify about prescribing practices for GLP-1 drugs in weight loss versus diabetes management
- Explain the dose-titration protocols and whether adequate warnings existed to guide prescribers
- Address the off-label use of semaglutide and liraglutide for weight loss before FDA approval for that indication
- Opine on whether the label warnings were sufficient for prescribers to make informed treatment decisions
- Discuss the standard of care for patient monitoring, follow-up, and discontinuation when GI symptoms develop
Pharmacology and Toxicology Experts
Pharmacologists and toxicologists address the drug mechanism and causation at a molecular level:
- Explain GLP-1 receptor pharmacology, including how synthetic agonists differ from endogenous GLP-1 in potency, half-life, and receptor binding
- Testify on the dose-response relationship between GLP-1 drug exposure and gastrointestinal motility impairment
- Address whether prolonged receptor activation can cause lasting changes to gastric nerve function or smooth muscle responsiveness
- Interpret the epidemiological literature linking GLP-1 use to GI outcomes
- Withstand Rule 702 challenges to the reliability and methodology of causation opinions
General Surgery Experts
General surgeons are relevant in cases involving cholecystectomy, bowel obstruction requiring surgical intervention, or feeding tube placement:
- Testify on the necessity and outcomes of surgical procedures resulting from alleged GLP-1 injuries
- Explain the perioperative risks associated with retained gastric contents in GLP-1 patients
- Address surgical complications and long-term quality-of-life impacts
What Attorneys Should Look for in Expert Selection
Mass tort pharmaceutical litigation demands experts who can hold up under aggressive cross-examination and survive Rule 702 challenges. Attorneys evaluating experts for GLP-1 cases should consider:
For gastroenterology experts:
- Board certification in gastroenterology with active clinical practice
- Experience diagnosing and treating gastroparesis, ileus, and bowel obstruction
- Familiarity with the GLP-1 mechanism of action and its effects on gastric motility
- Published research or clinical presentations on drug-induced GI motility disorders
- Prior expert witness or litigation experience in pharmaceutical cases
For endocrinology experts:
- Board certification in endocrinology with prescribing experience for GLP-1 medications
- Understanding of off-label prescribing practices and the regulatory timeline for weight loss indications
- Ability to speak to the adequacy of manufacturer warnings from a prescriber’s perspective
- Experience with case-specific causation analysis in pharmaceutical litigation
For pharmacology and toxicology experts:
- Advanced degree (PhD or MD) in pharmacology, toxicology, or a closely related field
- Published research on GLP-1 receptor pharmacology, gastrointestinal motility, or drug safety
- Prior experience with general causation testimony in pharmaceutical MDLs
- Ability to explain complex pharmacological mechanisms in language a jury can follow
- Prior Rule 702 / Daubert hearing experience with favorable rulings
Key Dates Attorneys Should Know
| Date | Event |
|---|---|
| February 2, 2024 | JPML centralizes GI injury cases into MDL 3094 (E.D. Pa.) |
| May 19, 2026 | Rule 702 expert exclusion motions and summary judgment motions filed |
| June 17, 2026 | Opposition briefs to Rule 702 motions due |
| June 30, 2026 | Opposition briefs to summary judgment motions due |
| July 15, 2026 | Reply briefs in support of Rule 702 motions due |
| August 7, 2026 | Reply briefs in support of summary judgment motions due |
| September 10-18, 2026 | Rule 702 hearings in Courtroom 16B (E.D. Pa.) |
| Ongoing | New cases filing monthly; 3,848 pending as of July 2026 |
The September 2026 Rule 702 hearings will determine which expert testimony is admissible and set the stage for bellwether trial selection. Attorneys building their cases now will have the strongest position when those rulings come down.
How Med Legal Pro Supports GLP-1 Litigation
Med Legal Pro connects attorneys with rigorously vetted gastroenterology, endocrinology, pharmacology, and general surgery expert witnesses who understand the science and clinical realities behind GLP-1 receptor agonist litigation. Our experts are matched to the specific demands of each case, not pulled from a generic database.
Whether you need a gastroenterologist to establish specific causation for gastroparesis, an endocrinologist to address prescribing practices, or a pharmacologist to survive a Rule 702 challenge, Med Legal Pro provides:
- Expert witness matching tailored to your case type and jurisdiction
- Case pre-screening to evaluate the strength of a GLP-1 injury claim before committing resources
- Medical record review and chronology to build the clinical timeline supporting causation
- C.L.E.A.R. Method™ expert reports designed for clarity and courtroom durability
With Rule 702 hearings weeks away and case volume still climbing, the attorneys who secure qualified expert support now will be positioned for the strongest outcomes.
Contact Med Legal Pro to discuss your GLP-1 case or request an expert consultation.
📞 (844) 633-5345 | ✉ experts@medlegalpro.com | 🌐 medlegalpro.com
Med Legal Pro LLC provides medical-legal litigation support to attorneys in personal injury, nursing home negligence, wrongful death, and mass tort cases nationwide. Medical Experience | Legal Knowledge | Professional Results.
Sources
1 Judicial Panel on Multidistrict Litigation, JPML Statistics Report (July 1, 2026). MDL 3094, In Re: Glucagon-like Peptide-1 Receptor Agonists (GLP-1 RAs) Products Liability Litigation, E.D. Pa. See also RX Index GLP-1 Lawsuits Tracker.
2 Memorandum, In Re: GLP-1 RAs Products Liability Litigation, MDL No. 3094, 24-md-3094 (E.D. Pa. Aug. 15, 2025) (Marston, J.). Available at govinfo.gov.
3 Sodhi M, Rezaeianzadeh R, Kezouh A, Bhatt DL. Risk of Gastrointestinal Adverse Events Associated With Glucagon-Like Peptide-1 Receptor Agonists for Weight Loss. JAMA. 2023;310(18):1915-1923. doi: 10.1001/jama.2023.19574
4 Health Canada, Updated Product Monographs for Ozempic (March 2024), Mounjaro and Trulicity (July 2024). Warnings and Precautions sections updated to include events of delayed gastric emptying and severe gastroparesis. See Mondaq summary.
5 Camilleri M. Clinical Consequences of Delayed Gastric Emptying With GLP-1 Receptor Agonists and Tirzepatide. Journal of Clinical Endocrinology and Metabolism. 2024. doi: PubMed 39418085.
