Mounjaro Side Effects

As of May 2026, some of the most common Mounjaro side effects reported to the FDA Adverse Event Monitoring System were injection site pain, nausea, diarrhea and vomiting.

The top reasons for reporting adverse events were that users took the drug for an off-label use or took an incorrect dose.

The most common Mounjaro side effects are gastrointestinal: nausea, diarrhea, vomiting, constipation, decreased appetite, indigestion and abdominal pain. These were reported by less than 5% of patients in Eli Lilly’s SURPASS clinical trials.

“Side effects are pretty similar between different GLP-1s,” Dr. Eldad Einav, cardiologist and obesity specialist, told Drugwatch. The GLP-1 agonist class includes semaglutide drugs like Ozempic and Wegovy, and tirzepatide drugs like Mounjaro and Zepbound.

“[The side effects] are considered a class effect, similar for all this class of medications,” Einav said.

Einav cited the SURPASS-2 trial, which compared tirzepatide and semaglutide head-to-head. The trial found that Mounjaro had a slightly higher rate of serious side effects than Ozempic.

“Switching to a different medication within the same class can sometimes improve tolerability for patients who experience side effects, due to variations in how individuals respond to specific drugs,” Einav said.

If you experience any persistent or bothersome side effects, speak to your health care provider.

Severe Mounjaro Side Effects

In rare cases, Mounjaro may cause severe side effects such as organ failure, low blood sugar, inflammation of the pancreas, diabetic retinopathy and gastroparesis. These conditions can be life-threatening.

Patients who experienced severe side effects after taking Mounjaro have filed lawsuits against Eli Lilly. Mounjaro lawsuits claim the drug caused gastroparesis and severe vomiting lasting for weeks despite treatment. They also claim that Eli Lilly failed to adequately warn about these and other possible adverse reactions.

Mounjaro has an FDA boxed warning, the agency’s highest level, because rodent studies showed a risk of thyroid C-cell tumors. The FDA says it is not known if Mounjaro causes these tumors in people. Patients who have a personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2) should not use Mounjaro.

If you take Mounjaro and experience signs of thyroid tumors — including hoarseness, lumps in the neck and difficulty swallowing — you should immediately report the symptoms to your doctor.

Most Mounjaro side effects resolve within several days. Patients are most likely to experience minor effects when first starting Mounjaro and after dosage increases. Some symptoms disappear during treatment as your body adjusts to the medicine.

Higher doses often contribute to greater chances of side effects and more severe symptoms. Patients have reported long-term side effects from Mounjaro, including vomiting that lasts for weeks. More serious side effects, such as severe digestive issues or pancreatitis, can be long-term.

Anyone experiencing extreme or lasting side effects should speak to their doctor immediately.

Mounjaro is considered safe for most patients who use it to treat Type 2 diabetes. Its FDA approval for this purpose indicates that its benefits outweigh the potential risks.

Even though Mounjaro may be generally safe for weight loss in overweight or obese individuals, it may cause malnutrition or muscle loss in average-weight or underweight people. Off-label use may increase risks. Eli Lilly and the experts Drugwatch talked to recommend avoiding Mounjaro for off-label use. Zepbound (tirzepatide), another Eli Lilly product, is FDA-approved for weight loss.

Discuss side effects with a doctor before taking Mounjaro and notify them if you experience any after starting tirzepatide treatment.

GLP-1 drugs like Mounjaro may increase the risk of NAION, a rare problem that can quickly cause lasting vision loss in one eye. A 2025 study in JAMA Network Open examined patients with Type 2 diabetes without prior eye problems. Those given semaglutide or tirzepatide had a higher risk of NAION and other optic nerve disorders, but the overall risk remained low.

NAION happens when the nerve that helps you see experiences reduced or blocked blood flow. This can cause sudden, painless vision loss in one eye, typically noticed upon waking. There is no proven cure, and most people do not fully recover their sight.

The FDA does not require a specific NAION warning on Mounjaro’s label. However, the label does say vision changes can be a side effect. If you notice blurring, dimming or sudden loss of vision, get help right away, even if the cause is unclear.

Sudden vision loss is an emergency. If you lose vision in one eye while taking Mounjaro, see an eye doctor or go to the emergency room right away.

Researchers Watching for Possible Choroidal Lymphoid Hyperplasia Risk

A May 2026 medical report in the New England Journal of Medicine highlighted two people who developed choroidal lymphoid hyperplasia after taking a GLP-1 drug. This is a rare and benign uveal lymphoid disorder, meaning it affects both the tissues of your eyes and your lymph nodes.

The patients lost vision in one eye after starting Trulicity (dulaglutide), a similar GLP-1 medication. Patients also experienced swollen lymph nodes. Their vision and swelling got better after they stopped the medicine. Doctors say this is extremely rare, and they are not sure why it happened. There are no reports of whether it may be a risk for all GLP-1 drugs.

Your health care provider can advise you on how to reduce your specific Mounjaro side effects. To alleviate gastrointestinal discomfort, limit fatty or spicy foods, eat slowly and stop when full.

Drinking chamomile tea or ginger ale and taking over-the-counter medications can help ease nausea. For constipation, eat high-fiber foods and drink lots of fluids.

If you’re experiencing Mounjaro side effects that last for more than a few days or interfere with your daily activities, it’s important to talk to your doctor.

Serious symptoms like difficulty breathing, severe abdominal pain, skin rash and vomiting require immediate medical attention. Even milder symptoms like vomiting and diarrhea can lead to dehydration. Consult your doctor if symptoms last for over a week.