FDA Flags Hundreds of Adverse Events Connected to Compounded GLP-1 Drugs
August 17th, 2025 // 10:30 pm @ jmpickett
Hundreds of people using compounded versions of popular GLP-1 medications — unapproved copies of brand-name weight-loss drugs like Wegovy, Ozempic, Mounjaro, and Zepbound — have reported side effects, some requiring hospitalization, FDA announced.
As of July 31, 2025, the agency had received 605 adverse event reports for compounded semaglutide and 545 reports for compounded tirzepatide, the FDA said. Regulators emphasized that the true number is likely higher, since many compounding pharmacies are not required to report side effects.
Dosing Errors a Major Concern
A significant share of reports stemmed from dosing mistakes with compounded semaglutide. Unlike brand-name GLP-1 drugs, which are packaged in prefilled pens that allow patients to simply “dial up” the prescribed dose, compounded products are often supplied in vials and drawn up with syringes.
“When patients have to fill their own syringes, there are more opportunities for dosing errors,” said Melanie Jay, MD, professor at NYU and director of the NYU Langone Comprehensive Program on Obesity Research.
In some cases, patients or providers administered incorrect amounts, or prescribed doses higher than those in FDA-approved versions. Reported side effects included nausea, vomiting, diarrhea, abdominal pain, constipation, and injection-site reactions. Several patients required medical treatment.
How Widespread Are the Risks?
The FDA has not disclosed how many people nationwide are taking compounded GLP-1s, making it difficult to assess the overall rate of adverse events.
“It’s really hard to get a handle on the actual number of prescriptions and adverse events,” said Jody Dushay, MD, an endocrinologist at Harvard Medical School and Beth Israel Deaconess Medical Center. “If I had to guess, this is the tip of the iceberg — not only in terms of adverse events, but also in terms of patients who aren’t benefiting from these medications.”
Adverse events may be underreported because patients often don’t inform prescribers or pharmacies when problems arise, Dushay added. Some sellers may also fail to notify the FDA.
Not Always the Drug Itself
The Alliance for Pharmacy Compounding (APC) cautioned that the FDA’s tally doesn’t prove compounded GLP-1s directly caused these issues. Some patients may have taken counterfeit or fraudulent products from unlicensed sources, rather than medicines prepared by legitimate compounding pharmacies.
Compounding pharmacies, licensed by state boards, are permitted to create customized medicines using the same active ingredients in FDA-approved drugs — often for patients who need nonstandard doses or when commercial products are unavailable, as was the case during past shortages of Wegovy and Ozempic.
