Mounjaro is a once-weekly tirzepatide injection approved for type 2 diabetes. Its safety record now includes a four-year heart-outcomes trial, and since August 2026 its label carries a second use: lowering the risk of heart attack, stroke and cardiovascular death in adults with type 2 diabetes at high risk of them [1].
Mounjaro is a type 2 diabetes drug, not a weight-loss drug, in the US
Mounjaro is approved to improve blood sugar, alongside diet and exercise, in adults and children 10 and older with type 2 diabetes. It's also approved to reduce the risk of major cardiovascular events in adults with type 2 diabetes who are at high risk for them [1].
Tirzepatide for weight is a different brand, Zepbound, which is approved for weight reduction and for moderate to severe obstructive sleep apnea in adults with obesity [2]. Pages written for other countries can describe different approved uses; this page follows the US label.
About 4 in 10 people on the highest dose had a digestive side effect
In the label's placebo-controlled trials, digestive side effects hit 37.1%, 39.6% and 43.6% of people on the 5, 10 and 15 mg doses, against 20.4% on placebo [1]. The label says most nausea, vomiting and diarrhea happened while the dose was going up "and decreased over time."
| Side effect | Placebo | 5 mg | 10 mg | 15 mg |
|---|---|---|---|---|
| Nausea | 4 | 12 | 15 | 18 |
| Diarrhea | 9 | 12 | 13 | 17 |
| Decreased appetite | 1 | 5 | 10 | 11 |
| Vomiting | 2 | 5 | 5 | 9 |
| Constipation | 1 | 6 | 6 | 7 |
| Indigestion | 3 | 8 | 8 | 5 |
| Stomach pain | 4 | 6 | 5 | 5 |
Mounjaro prescribing information, Table 1, August 2026 version. Doses are the label's maintenance strengths, shown for comparison only.
Digestive side effects led 3.0%, 5.4% and 6.6% of people on the three doses to stop, against 0.4% on placebo [1]. Injection-site reactions were reported by 3.2% vs 0.4%. The full side-effect picture for both tirzepatide brands is in tirzepatide side effects.
The serious risks on the label are mostly uncommon
Mounjaro's Warnings section lists ten risks. Most are uncommon, and several apply only in specific situations, such as taking insulin or having surgery. Here is each one with the number the label gives.
| Risk | How often (label) | Signs or situation | Section |
|---|---|---|---|
| Thyroid C-cell tumors | Seen in rats; unknown in people | Lump or swelling in the neck, hoarseness, trouble swallowing, shortness of breath | Boxed warning; 5.1 |
| Acute pancreatitis | 0.23 vs 0.11 patients per 100 years of exposure (vs comparators) | Severe stomach pain that won't go away, sometimes reaching the back | 5.2 |
| Low blood sugar | 0% on Mounjaro alone (below 54 mg/dL); 14% to 19% with basal insulin vs 13% on placebo | More likely with insulin or a sulfonylurea | 5.3; Table 2 |
| Allergic reactions | 3.2% vs 1.7% on placebo; anaphylaxis and angioedema reported after approval | Swelling of face, lips, tongue or throat; trouble breathing or swallowing; severe rash | 5.4 |
| Kidney injury from dehydration | Reported after approval, sometimes needing dialysis | Follows vomiting, diarrhea or nausea that drains fluids | 5.5 |
| Severe digestive reactions | 1.3%, 0.4% and 1.2% on the three doses vs 0.9% on placebo | Not recommended with severe gastroparesis | 5.6 |
| Diabetic eye disease getting worse | Temporary worsening reported with fast blood-sugar improvement | Applies to people with existing diabetic retinopathy | 5.7 |
| Gallbladder disease | 0.6% vs 0% on placebo | Upper stomach pain, fever, yellowing of skin or eyes, clay-colored stools | 5.8 |
| Aspiration under anesthesia | Rare reports with GLP-1 drugs | Tell your surgical team you take it | 5.9 |
| Pen sharing | Never share a KwikPen, even with a new needle | Risk of blood-borne infection | 5.10 |
Mounjaro prescribing information, August 2026 version.
The thyroid warning works the same way it does for semaglutide: rat studies, with human relevance not determined [1]. The human evidence for GLP-1 drugs is laid out in Wegovy and thyroid cancer.
Against another GLP-1 drug, Mounjaro was at least as safe for the heart
SURPASS-CVOT randomized 13,299 adults with type 2 diabetes and established heart disease to Mounjaro or dulaglutide, another GLP-1 drug already approved for heart-risk reduction, and followed them for a median of 210 weeks, about four years [1]. The comparison was another active drug, not a placebo. The trial's lead sponsor was Eli Lilly and Company, Mounjaro's maker [3].
| Outcome | Dulaglutide (6,647) | Mounjaro (6,647) | Hazard ratio (CI) | Note |
|---|---|---|---|---|
| Heart attack, stroke or cardiovascular death | 863 (13.0%) | 803 (12.1%) | 0.92 (0.83 to 1.01) | Non-inferior; superiority not established |
| Cardiovascular death | 409 (6.2%) | 367 (5.5%) | 0.89 (0.77 to 1.02) | Not controlled for multiple testing |
| Death from any cause | 670 (10.1%) | 567 (8.5%) | 0.84 (0.75 to 0.94) | Not controlled for multiple testing |
Mounjaro prescribing information, section 14.6, Table 10. Sponsor: Eli Lilly and Company. The label footnotes the secondary rows as "Not controlled for family-wise type I error rate," so treat them as supportive, not proof.
What this does and doesn't show: Mounjaro wasn't worse than a drug with proven heart benefit, over about four years. It didn't prove better on the main outcome. The lower death rate is encouraging but, by the label's own footnote, not a tested claim [1].
No trial has compared Mounjaro and Ozempic head to head for safety
The closest is SURPASS-2, a 40-week open-label trial of 1,879 people with type 2 diabetes that compared three tirzepatide doses with semaglutide 1 mg, the drug in Ozempic. It was designed to compare blood-sugar control, and it was funded by Eli Lilly [4]. Digestive side effects looked similar: nausea in 17% to 22% on tirzepatide vs 18% on semaglutide, diarrhea 13% to 16% vs 12%, vomiting 6% to 10% vs 8%. Serious adverse events were reported in 5% to 7% on tirzepatide vs 3% on semaglutide [4]. For Ozempic's own warnings, see Ozempic safety and side effects.
Who should not take Mounjaro
People with a personal or family history of medullary thyroid carcinoma or MEN 2, or a serious allergy to tirzepatide or the product's ingredients, shouldn't take it [1]. The label also says it isn't recommended for people with severe gastroparesis.
- Pregnancy. The label says human data are insufficient to judge the risk of birth defects or miscarriage; animal studies showed effects on the fetus, and poorly controlled diabetes carries its own risks in pregnancy. It should be used in pregnancy only if the benefit justifies the risk [1].
- Breastfeeding. In a single-dose study, tirzepatide in breast milk was "either undetectable or low," and there are "no available data" on effects on the baby or on milk production [1]. Your prescriber weighs this with you.
- Diabetic eye disease. People with existing retinopathy should be monitored, because fast improvement in blood sugar can temporarily worsen it [1].
Mounjaro can make birth-control pills less reliable for a few weeks
Mounjaro slows stomach emptying, which can reduce how well birth-control pills are absorbed. The label says the delay "is largest after the first dose and diminishes over time" [1].
Is Mounjaro safe for weight loss?
It isn't approved for weight loss in the US; tirzepatide for weight is Zepbound. The two contain the same molecule, so the warnings largely overlap, but the approved uses, trials and labels differ [2]. For Zepbound's side effects, see Zepbound side effects. Compounded tirzepatide has extra questions about quality; see is compounded tirzepatide safe and the compounded tirzepatide guide.
Body aches and blood clots aren't on Mounjaro's label
Neither is listed. A search of Mounjaro's full prescribing information finds no mention of muscle aches, joint pain, blood clots or embolism [1]. If you have new aches or other new symptoms, get them checked either way; the cause may be unrelated to the drug. Peeing, thirst and sweating questions are in does Mounjaro make you pee more.
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