Short answer: In the label's placebo-controlled trials, the most common Mounjaro side effects were nausea (12% to 18% vs 4% on placebo), diarrhea (12% to 17% vs 9%), decreased appetite (5% to 11% vs 1%), vomiting, constipation, indigestion and stomach pain. Most nausea, vomiting and diarrhea happened while the dose was being raised and eased over time. Mounjaro has a boxed warning about thyroid C-cell tumors.
What Mounjaro is approved for: Mounjaro is approved, along with diet and exercise, to improve blood sugar control in adults and children 10 years and older with type 2 diabetes, and to lower the risk of major heart and blood vessel events in adults with type 2 diabetes at high risk of them (section 1).
Source
MOUNJARO (tirzepatide) injection, prescribing information and Medication Guide. Eli Lilly. DailyMed, version published September 2, 2026. DailyMed setid d2d7da5d-ad07-4228-955f-cf7e355c8cc0
WARNING: RISK OF THYROID C-CELL TUMORS
In rats, tirzepatide caused thyroid C-cell tumors. It is not known whether Mounjaro causes these tumors, including medullary thyroid carcinoma (MTC), in people. Mounjaro must not be used by anyone with a personal or family history of MTC or with Multiple Endocrine Neoplasia syndrome type 2 (MEN 2), and the label lists a neck lump, trouble swallowing, shortness of breath or lasting hoarseness as symptoms to report.
These are the label's own numbers from the Adverse Reactions section. Where the label compares with placebo (a dummy treatment), both columns are shown, so you can see how much more often a reaction happened on Mounjaro.
| Adverse reaction | Placebo (N=235) % | Mounjaro 5 mg (N=237) % | Mounjaro 10 mg (N=240) % | Mounjaro 15 mg (N=241) % |
|---|---|---|---|---|
| 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 |
| Dyspepsia | 3 | 8 | 8 | 5 |
| Abdominal Pain | 4 | 6 | 5 | 5 |
Two placebo-controlled trials (SURPASS-1 and SURPASS-5) in adults with type 2 diabetes; 718 people on Mounjaro for a mean of 36.6 weeks. Percentages are people who reported the reaction at least once. Hypoglycemia is reported separately.
Stomach and gut reactions overall: placebo 20.4%, Mounjaro 5 mg 37.1%, 10 mg 39.6% and 15 mg 43.6%. Stopping treatment because of them: 3.0%, 5.4% and 6.6% on the three doses vs 0.4% on placebo. Most nausea, vomiting and diarrhea happened during dose escalation and decreased over time.
Less common gut reactions (placebo; 5 mg; 10 mg; 15 mg): burping 0.4%, 3.0%, 2.5%, 3.3%; gas 0%, 1.3%, 2.5%, 2.9%; acid reflux 0.4%, 1.7%, 2.5%, 1.7%; bloating 0.4%, 0.4%, 2.9%, 0.8%.
Injection site reactions: 3.2% on Mounjaro vs 0.4% on placebo in the placebo-controlled trials.
In a heart outcomes trial of 6,647 adults, reactions were similar except dysesthesia (0.7%), decreased appetite (17%), constipation (13%), vomiting (12%), stomach pain (10%) and fatigue (10%).
Gallbladder problems (gallstones, biliary colic, gallbladder removal) were reported by 0.6% of people on Mounjaro and 0% on placebo.
The Warnings and Precautions part of the label lists these. Each line gives the label's heading and what it means in plain words.
Risk of thyroid C-cell tumors. The boxed warning risk: thyroid tumors seen in rats. Not for people with a personal or family history of MTC or with MEN 2.
Acute pancreatitis. Inflammation of the pancreas, including fatal cases, has been seen. Signs include severe stomach pain that will not go away, sometimes spreading to the back, with or without vomiting. If it is suspected, Mounjaro is stopped.
Low blood sugar with insulin or sulfonylureas. Taking Mounjaro with insulin or a sulfonylurea raises the risk of low blood sugar, including severe episodes. The label says lowering the dose of those medicines may reduce the risk.
Serious allergic reactions. Anaphylaxis and angioedema (swelling of the face, lips, tongue or throat) have been reported. If one happens, Mounjaro is stopped.
Kidney injury from fluid loss. Kidney injury, sometimes needing dialysis, has been reported, mostly in people who lost fluids from nausea, vomiting or diarrhea. Kidney function is checked in people with these reactions, especially when starting or raising the dose.
Severe stomach and gut reactions. Gut side effects can be severe. Mounjaro is not recommended for people with severe gastroparesis (very slow stomach emptying).
Diabetic eye disease. Fast improvement in blood sugar has been linked to temporary worsening of diabetic retinopathy. People with a history of it should be monitored.
Gallbladder disease. Gallstones and gallbladder inflammation have been reported. If gallstones are suspected, the label calls for gallbladder tests.
Breathing in stomach contents during anesthesia. Mounjaro slows stomach emptying. Rare cases of pulmonary aspiration under general anesthesia or deep sedation have been reported with this drug class, so the label says to tell the care team you use it before any procedure.
Never share a KwikPen. A Mounjaro KwikPen must never be shared between people, even with a new needle, because of the risk of passing on blood-borne infections.
From the Medication Guide that comes with Mounjaro:
Dose Track has a side-effect log. Each entry records the symptom, a severity (none, mild, moderate, severe or life-threatening), the date and an optional note, and can be tied to a specific dose or logged on its own. The history screen shows what you logged over time, which makes it easier to tell your prescriber when a reaction started and whether it is easing. The app records what you enter; it does not judge whether a symptom is serious. For anything on the label's call-your-doctor list, call your doctor.
This page is what the FDA label says, in plain words. It is not medical advice. Follow your prescriber, and ask them or your pharmacist about anything here.