Boxed warningIn rats, tirzepatide caused thyroid C-cell tumors; whether Mounjaro causes them in people, including medullary thyroid carcinoma (MTC), is unknown. Mounjaro must not be used with a personal or family history of MTC or with MEN 2.[1]
Mounjaro side effects by dose
Mounjaro's label lists seven side effects that affected at least 5% of people in its placebo-controlled diabetes trials, all digestive or appetite-related, and most rose with dose.[1]
| 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% |
| Dyspepsia | 3% | 8% | 8% | 5% |
| Abdominal pain | 4% | 6% | 5% | 5% |
| Eructation (burping) | 0.4% | 3% | 2.5% | 3.3% |
| Gastroesophageal reflux (GERD) | 0.4% | 1.7% | 2.5% | 1.7% |
| Flatulence | 0% | 1.3% | 2.5% | 2.9% |
| Abdominal distension | 0.4% | 0.4% | 2.9% | 0.8% |
The first seven rows are the label's main table (reactions in at least 5% of people); the last four are the less common stomach effects the label reports in its text.[1] Across seven longer trials, the types and rates of common side effects were similar.[1]
Each common Mounjaro side effect
Every common Mounjaro side effect is digestive except decreased appetite, and the label adds detail on several of them.[1]
Mounjaro nausea and vomiting
Nausea affected 12%, 15%, 18% of people on 5, 10 and 15 mg (placebo 4%), and vomiting 5%, 5%, 9% (placebo 2%).[1] The label says most nausea, vomiting and diarrhea “occurred during dose escalation and decreased over time.”[1]
Mounjaro diarrhea
Diarrhea affected 12–17% of people on Mounjaro against 9% on placebo, highest at 15 mg (17%).[1] With vomiting, it can lead to fluid loss; the label warns that dehydration can cause acute kidney injury and asks people to report diarrhea or vomiting that does not stop.[1]
Mounjaro constipation
Constipation affected 6–7% of people versus 1% on placebo in the diabetes trials, and 13% in the 4-year heart outcomes trial.[1] Reports after approval include severe constipation with fecal impaction, ileus and intestinal obstruction.[1]
Mounjaro heartburn, indigestion and burping
Heartburn-type symptoms were less common than nausea: indigestion (dyspepsia) affected 5–8% versus 3%, reflux (GERD) 1.7–2.5% versus 0.4%, and burping 2.5–3.3% versus 0.4%.[1] The label does not use the word “heartburn”; these are the terms it reports.
Mounjaro hair loss
Hair loss is not in Mounjaro's trial tables; it appears in the label's list of reports after approval (“alopecia”), where the rate cannot be estimated.[1] In the Zepbound weight-loss trials of the same drug, hair loss affected 4–5% versus 1% on placebo, mostly women (7.1% vs 0.5% of men).[2]
Mounjaro pancreatitis
Confirmed acute pancreatitis was uncommon but more frequent than on comparators: 14 events in 13 people on Mounjaro (0.23 per 100 patient-years) versus 3 events (0.11 per 100 patient-years).[1] Mounjaro also raised the pancreatic enzymes amylase (33–38%) and lipase (31–42%) on average; the label says the meaning of those rises without symptoms is unknown.[1]
How long do Mounjaro side effects last?
Most Mounjaro stomach side effects start in the weeks after a dose increase and then fade: the label says nausea, vomiting and diarrhea mostly “occurred during dose escalation and decreased over time.”[1]
| Weeks | Dose | What the label says |
|---|---|---|
| 1–4 | 2.5 mg | Starting dose; since August 2026 also allowed for ongoing glucose control |
| 5–8 | 5 mg | First possible increase |
| 9 and later | 7.5 mg, 10 mg, 12.5 mg, 15 mg | Further 2.5 mg steps, each after at least 4 weeks on the current dose |
| 21 at the earliest | 15 mg | Maximum dose |
Each step is a new period when side effects can return, so the shortest path to 15 mg holds about 20 weeks of possible escalation effects.[1] The full schedule is on the Mounjaro dosage chart, and a week-by-week view for the same drug is on how long do Zepbound side effects last.
Mounjaro long-term side effects
In the longest Mounjaro trial, SURPASS-CVOT, 6,647 adults with type 2 diabetes and heart disease took Mounjaro for a median follow-up of 210.1 weeks (about 4 years), and side effects were similar to the shorter trials.[1]
| Finding | Result |
|---|---|
| Side effects more common than in the short trials | Decreased appetite 17%, constipation 13%, vomiting 12%, abdominal pain 10%, fatigue 10%, dysesthesia 0.7% |
| Major heart events vs dulaglutide | Hazard ratio 0.92 (95.3% CI 0.83–1.01): non-inferior; superiority not shown |
| Comparator | Dulaglutide 1.5 mg weekly (13,299 people randomized in total) |
The label's long-term risks are the boxed thyroid warning from rat studies, pancreatitis, acute gallbladder disease (0.6% vs 0% on placebo), kidney injury from dehydration, and worsening diabetic eye disease in people with a history of diabetic retinopathy.[1] In November 2026 the FDA also required all GLP-1 drug labels, Mounjaro included, to warn about NAION, a rare cause of sudden vision loss in one eye.[4] On the basis of this trial, the FDA approved Mounjaro in August 2026 to reduce cardiovascular risk in adults with type 2 diabetes and heart disease.[3]
Low blood sugar on Mounjaro
Mounjaro alone rarely caused low blood sugar in the trials, but rates rose when it was added to insulin or a sulfonylurea.[1]
| Trial | Placebo | 5 mg | 10 mg | 15 mg |
|---|---|---|---|---|
| Mounjaro alone (40 weeks) | 1% | 0% | 0% | 0% |
| Added to basal insulin (40 weeks) | 13% | 16% | 19% | 14% |
| With a sulfonylurea (up to 104 weeks) | — | 13.8% | 9.9% | 12.8% |
Severe low blood sugar, needing another person's help, occurred in 0–2% with basal insulin and 0–0.6% with a sulfonylurea.[1] The label says to consider lowering the insulin or sulfonylurea dose when Mounjaro is started.[1]
Other measured effects
Several smaller effects are reported in the label text rather than the main table.[1]
- Injection-site reactions: 3.2% vs 0.4% on placebo; see injection sites.
- Allergic (hypersensitivity) reactions: 3.2% vs 1.7%, sometimes severe, such as hives and eczema.
- Heart rate: up 2 to 4 beats per minute on average (placebo 1); episodes of fast heart rate in 4.6%, 5.9% and 10% on 5, 10 and 15 mg vs 4.3%.
- Skin sensations and taste: dysesthesia 0.4% on each dose vs 0%; altered taste 0.1% vs 0%.
Mounjaro side effects in children 10 and older
In 97 children and teenagers with type 2 diabetes treated for a mean of 39.9 weeks, side effects matched those in adults except for more vomiting, abdominal pain and low blood sugar.[1] Over the 30-week placebo-controlled period, vomiting affected 16% (5 mg) and 12% (10 mg) versus 3% on placebo, and abdominal pain 22% and 15% versus 9%; no severe low blood sugar was reported.[1]
When to call a doctor about Mounjaro side effects
The Mounjaro label names the warning signs that need prompt medical attention; severe stomach side effects affected 0.4–1.3% of people on Mounjaro versus 0.9% on placebo.[1]
| Problem | Signs the label describes | What the label says |
|---|---|---|
| Acute pancreatitis | Persistent or severe abdominal pain, sometimes spreading to the back, with or without nausea or vomiting | Stop Mounjaro if suspected |
| Serious allergic reaction | Anaphylaxis or angioedema (swelling) | Stop Mounjaro and treat promptly |
| Kidney injury from dehydration | Nausea, vomiting or diarrhea leading to fluid loss | Kidney function monitored, especially while the dose is raised |
| Acute gallbladder disease | Gallstones or gallbladder inflammation | Gallbladder tests and follow-up if suspected |
| Diabetic eye disease | Temporary worsening of diabetic retinopathy with rapid glucose improvement | Monitoring for people with a history of retinopathy |
| Low blood sugar | With insulin or a sulfonylurea | Lower doses of those medicines may be needed |
| Surgery or sedation | Risk of breathing in stomach contents | Tell the care team about Mounjaro before a procedure |
| Sudden vision loss in one eye (NAION)[4] | Painless decreased or blurred vision in one eye | FDA class warning added November 2026; contact a health care professional right away |
Who should not take Mounjaro
The label says Mounjaro must not be used by people with a personal or family history of medullary thyroid carcinoma, by people with MEN 2, or by anyone with a known serious allergy to tirzepatide or the product's ingredients.[1] It is also “not recommended in patients with severe gastroparesis,” and anaphylaxis and angioedema have been reported.[1]
Mounjaro vs Zepbound side effects
Mounjaro and Zepbound are the same drug, tirzepatide, but nausea was about twice as common in the Zepbound weight trials (25–29%) as in the Mounjaro diabetes trials (12–18%).[2][1] Every Mounjaro and Zepbound rate on this page is also in a downloadable file, tirzepatide-side-effects.csv. The two labels side by side, with a nausea chart, are on tirzepatide side effects; Zepbound's own table is on Zepbound side effects.
Related
- Mounjaro dosage chartDoses, steps and children
- Zepbound vs MounjaroSame molecule, different labels
- Tirzepatide side effectsBoth labels side by side
Frequently asked questions
What are the most common side effects of Mounjaro?
Nausea, diarrhea, decreased appetite, vomiting, constipation, indigestion and abdominal pain. Nausea affected 12–18% of people on 5–15 mg versus 4% on placebo.[1]
How long do Mounjaro side effects last?
The label says most nausea, vomiting and diarrhea occurred during dose escalation and decreased over time. Escalation to 15 mg takes at least 20 weeks, in 4-week steps.[1]
Does Mounjaro cause hair loss?
Can Mounjaro cause pancreatitis?
Yes, rarely: confirmed pancreatitis occurred at 0.23 per 100 patient-years on Mounjaro versus 0.11 on comparators. Severe stomach pain that does not go away needs prompt medical attention.[1]
Does Mounjaro cause heartburn?
The label reports indigestion in 5–8% versus 3% on placebo and reflux in 1.7–2.5% versus 0.4%; it does not use the word heartburn.[1]
Who should not take Mounjaro?
People with a personal or family history of medullary thyroid carcinoma or MEN 2, and people with a known serious allergy to tirzepatide or its ingredients. It is not recommended in severe gastroparesis.[1]
What are Mounjaro withdrawal symptoms?
The Mounjaro label describes no withdrawal syndrome. Tirzepatide has a half-life of about 5 days, so it clears from the body over several weeks after the last dose.[1]
What are the long-term side effects of Mounjaro?
In a trial with a median of 210 weeks, side effects were similar to shorter trials, with decreased appetite in 17% and constipation in 13%. Long-term label warnings include pancreatitis, gallbladder disease and a thyroid tumor warning from rat studies.[1]
Sources
- Mounjaro (tirzepatide) injection: prescribing information and Instructions for Use
- Zepbound (tirzepatide) injection: prescribing information, Medication Guide and Instructions for Use
- FDA approves Lilly's Mounjaro to reduce cardiovascular risk in adults with type 2 diabetes
- FDA requires safety labeling changes for GLP-1 receptor agonists due to potential increased risk of rare but serious eye condition (NAION)