Side effects
Mounjaro side effects
Mounjaro's most common side effects in the FDA label are nausea, diarrhea, decreased appetite, vomiting, constipation, indigestion and stomach pain.1 Nausea affected 12% to 18% of adults on 5 to 15 mg against 4% on placebo, mostly while the dose was being raised.1 The label carries a boxed warning for thyroid C-cell tumors seen in rats.1
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Where these numbers come from
Most rates below come from the label's pool of two placebo-controlled trials in adults with type 2 diabetes (SURPASS-1 and SURPASS-5), in which 718 people took Mounjaro 5 mg, 10 mg or 15 mg once weekly.1 The placebo column shows how often the same complaint turned up without the drug, so the gap between columns matters more than either number alone. Separate figures come from the heart outcomes trial, the trial in children and reports made after approval.
Stomach and gut effects
These are the most frequent side effects. Nausea, diarrhea, decreased appetite and vomiting were each most frequent at 15 mg.1
| Side effect | 5 mg | 10 mg | 15 mg | Placebo |
|---|---|---|---|---|
| Nausea1 | 12% | 15% | 18% | 4% |
| Diarrhea1 | 12% | 13% | 17% | 9% |
| Decreased appetite1 | 5% | 10% | 11% | 1% |
| Vomiting1 | 5% | 5% | 9% | 2% |
| Constipation1 | 6% | 6% | 7% | 1% |
| Indigestion (dyspepsia)1 | 8% | 8% | 5% | 3% |
| Abdominal pain1 | 6% | 5% | 5% | 4% |
| Any stomach or gut effect1 | 37.1% | 39.6% | 43.6% | 20.4% |
| Stopped treatment because of one1 | 3.0% | 5.4% | 6.6% | 0.4% |
| Severe stomach or gut effect1 | 1.3% | 0.4% | 1.2% | 0.9% |
Most nausea, vomiting and diarrhea happened while the dose was being raised and became less frequent over time.1 Smaller groups reported burping (2.5% to 3.3% against 0.4% on placebo), gas (1.3% to 2.9% against 0%), reflux (1.7% to 2.5% against 0.4%) and bloating (0.4% to 2.9% against 0.4%).1 The label does not recommend Mounjaro for people with severe gastroparesis, in which the stomach empties very slowly.1
Low blood sugar
The risk depends on what Mounjaro is combined with, and it is higher with a sulfonylurea or insulin.1
| Used with | Glucose below 54 mg/dL | Severe episodes |
|---|---|---|
| Nothing else, 40 weeks1 | 0% at every dose, against 1% on placebo | None |
| Basal insulin1 | 16% (5 mg), 19% (10 mg), 14% (15 mg), against 13% on placebo | 0%, 2% and 1%, against 0% |
| A sulfonylurea, up to 104 weeks1 | 13.8%, 9.9% and 12.8% | 0.5%, 0% and 0.6% |
When Mounjaro is started, the label tells prescribers to consider lowering the dose of a sulfonylurea or insulin.1 How it acts on glucose is covered in Mounjaro and blood sugar.
Less common effects and lab changes
- Injection site reactions: 3.2% against 0.4% on placebo.1
- Allergic-type reactions: 3.2% against 1.7%, sometimes severe, such as hives and eczema.1
- Faster heart rate: an average rise of 2 to 4 beats per minute, against 1 on placebo; the clinical meaning is uncertain.1
- Gallbladder disease (gallstones, biliary colic, gallbladder removal): 0.6% against 0%.1
- Acute pancreatitis: 14 confirmed events in 13 patients, or 0.23 patients per 100 years of exposure, against 0.11 on comparator drugs.1
- Abnormal skin sensation (dysesthesia): 0.4% at each dose against 0%; altered taste (dysgeusia): 0.1% against 0%.1
- Pancreatic enzymes: on average, amylase rose 33% to 38% and lipase 31% to 42% from baseline; without other signs of pancreatitis, the meaning is unknown.1
- Antibodies: 51% of adults (2,570 of 5,025) in seven trials made antibodies to tirzepatide. Drug levels and effectiveness showed no clinically significant change, but injection site and allergic reactions were more common in people with antibodies.1
In the heart trial and in children
SURPASS-CVOT gave Mounjaro to 6,647 adults. Side effects matched the earlier trials, except for these rates: decreased appetite 17%, constipation 13%, vomiting 12%, abdominal pain 10%, fatigue 10% and dysesthesia 0.7%.1
Children 10 and older had more vomiting, abdominal pain and low blood sugar than adults. Over 30 weeks, vomiting affected 16% on 5 mg and 12% on 10 mg against 3% on placebo, and abdominal pain 22% and 15% against 9%.1
Reported after approval
Reports sent in after Mounjaro reached the market cannot give a frequency.1 They include anaphylaxis and angioedema; pancreatitis, including fatal hemorrhagic or necrotizing cases; ileus, intestinal obstruction and severe constipation with fecal impaction; aspiration of stomach contents during anesthesia; acute kidney failure; and hair loss.1
Warnings in the label
Boxed warning: thyroid C-cell tumors
In male and female rats, tirzepatide caused thyroid C-cell tumors that grew more common with dose and treatment length, at exposures relevant to people.1 Whether it causes these tumors, including medullary thyroid carcinoma, in humans is unknown.1 Patients are told to report a neck lump, trouble swallowing, shortness of breath or lasting hoarseness.1 Routine calcitonin tests and thyroid ultrasound are of uncertain value for early detection.1
Other warnings
- Pancreatitis: Mounjaro is stopped if it is suspected, for example persistent severe stomach pain that may spread to the back.1
- Kidney injury: seen mostly in people dehydrated by nausea, vomiting or diarrhea, and some cases needed dialysis.1
- Diabetic eye disease: fast improvement in blood sugar has been linked to temporary worsening of retinopathy, so people with a history of it are monitored.1
- Gallbladder: signs include upper stomach pain, fever, yellow skin or eyes and clay-colored stools.1
- Anesthesia: because stomach emptying slows, rare aspiration has been reported with GLP-1 receptor agonists during anesthesia or deep sedation.1
- Birth control pills: in one study a single 5 mg dose cut peak hormone levels by 55% to 66%. The label advises a non-oral or added barrier method for 4 weeks after starting and after each dose increase.1
- Other pills: absorption can change, so narrow-margin drugs such as warfarin need monitoring.1
- Pregnancy and breastfeeding: human data are too few to judge risk; in rats and rabbits, fetal growth fell, and rats also showed malformations, at doses that cut the mothers' weight and food intake.1 In 11 breastfeeding women given one 5 mg dose, tirzepatide was undetectable in 164 of 171 milk samples.1
- Older adults: no overall difference in safety or effectiveness was seen at 65 and older.1
Related pages
The Mounjaro profile covers the medicine as a whole. The label's gradual dose steps are meant to limit stomach effects,1 and they are laid out on Mounjaro dosage. What the trials found is on Mounjaro benefits and uses, and pen handling is on Mounjaro injection sites and pen use. Effects shared across the drug class are compared in GLP-1 side effects.
More on Mounjaro
Mounjaro dosage
Published dosing information for Mounjaro from labels and studies, with its source, and why it is not advice for you.
Mounjaro injection sites and pen use
Where Mounjaro is injected, how the pen is used, and site rotation, from the FDA label and Instructions for Use. Sourced and reviewed.
Mounjaro benefits and uses
What published sources report about Mounjaro and its uses, with the evidence level of each finding. No promises.
Frequently asked questions
Who cannot take Mounjaro?
The label says Mounjaro must not be used by people with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2), or by anyone with a known serious allergy to tirzepatide or its ingredients.1 It is not recommended for people with severe gastroparesis, and its safety and effectiveness are not established in children under 10.1 Pregnancy, breastfeeding and a history of diabetic eye disease each call for a discussion with the prescriber first.1
What are long-term side effects of Mounjaro?
The longest trial in the label, SURPASS-CVOT, followed 13,299 adults for a median of 210.1 weeks, about four years.1 Side effects there matched the shorter trials, apart from rates such as decreased appetite 17%, constipation 13% and vomiting 12% among the 6,647 people on Mounjaro.1 The open long-term question is the boxed warning: tirzepatide caused thyroid C-cell tumors in rats, and whether it does so in humans is unknown.1
Which is safer, Ozempic or Mounjaro?
The sources here give no single verdict, but they allow a side-by-side look. In SURPASS-2, which compared tirzepatide with semaglutide 1 mg (an Ozempic dose) for 40 weeks, nausea affected 17% to 22% against 18%, diarrhea 13% to 16% against 12%, and vomiting 6% to 10% against 8%.23 Both labels carry a boxed warning for thyroid C-cell tumors seen in rodents.13 Both also warn of pancreatitis, gallbladder disease and low blood sugar when combined with insulin or a sulfonylurea.13
Does Mounjaro cause depression or suicidal thoughts?
FDA's review found no increased risk. A meta-analysis of 91 placebo-controlled trials with 107,910 patients showed no rise in suicidal thoughts or behavior, or in anxiety, depression, irritability or psychosis, with GLP-1 receptor agonist medicines.4 In January 2026 FDA asked for that warning to be removed from the Saxenda, Wegovy and Zepbound labels; labels of the GLP-1 medicines approved for blood sugar control in type 2 diabetes did not include it.4 FDA still advises anyone with new or worsening depression to tell a health care professional.4
Written by D2C Peptides Editorial Team.
Pending qualified review.
Updated .
Sources
- MOUNJARO (tirzepatide) injection Prescribing Information, Medication Guide and Instructions for Use, revised 08/2026 (NDA 215866/S-044, S-045). U.S. Food and Drug Administration (Drugs@FDA), 2026.
- SURPASS-2 abstract: adverse events (PMID 34170647). New England Journal of Medicine (via NLM PubMed E-utilities), 2021.
- OZEMPIC (semaglutide) injection, prescribing information (revised 5/2026). U.S. National Library of Medicine, DailyMed (label by Novo Nordisk), 2026.
- FDA Requests Removal of Suicidal Behavior and Ideation Warning from Glucagon-Like Peptide-1 Receptor Agonist (GLP-1 RA) Medications (Drug Safety Communication, 01-13-2026). U.S. Food and Drug Administration, 2026.