Mounjaro Side Effects: Rare but Serious Adverse Events
HealthRX.com
Serious Mounjaro reactions are rare but need fast action
Key numbers
- 1.3%Severe GI reactions on 5 mg in placebo-controlled trials (placebo 0.9%)Source: dailymed.nlm.nih.gov, as cited Oct 30, 2026
- 3.0%Stopped treatment for GI reasons on 5 mg (placebo 0.4%)Source: dailymed.nlm.nih.gov, as cited Oct 30, 2026
- 0.6%Gallbladder disease in Mounjaro-treated adults (placebo 0%)Source: dailymed.nlm.nih.gov, as cited Oct 30, 2026
From the public record
Most reported events in FDA adverse event reports for tirzepatide
Through 2026-10-28, FDA had received 181,060 adverse event reports for tirzepatide, 33,095 of them marked serious by the reporter. The symptom terms named most often were nausea (19,737), injection site pain (14,615) and diarrhoea (11,312).
| Measure | Value | Note |
|---|---|---|
| All reports received | 181,060 | |
| Reports the reporter marked serious | 33,095 | death, hospitalisation, disability or similar outcome |
| Nausea | 19,737 reports | |
| Injection site pain | 14,615 reports | |
| Diarrhoea | 11,312 reports | |
| Vomiting | 9,395 reports | |
| Constipation | 7,625 reports |
How this was calculated
Counted FAERS reports listing this active substance, then the reaction terms named most often. A report can name several reactions, and a term can describe the illness being treated and not an effect of the drug. Terms about product use or complaints rather than symptoms (for example incorrect dose administered) were left out of the list.
Reports where FDA recorded tirzepatide as a single-ingredient active substance (any brand, not only Mounjaro), all years to 2026-10-28
FAERS reports are unverified and do not prove the drug caused the event. Reporting rises with use, publicity and lawsuits, so these counts cannot give rates or risks and cannot be compared between drugs.
From the public record
FDA label facts for tirzepatide
The FDA label read for tirzepatide (Mounjaro, application NDA215866) was last revised on 2026-08-27. It carries a boxed warning headed "WARNING: RISK OF THYROID C-CELL TUMORS". Of the 4 population sections checked, 4 are present: pregnancy, lactation, pediatric use, geriatric use.
| Measure | Value | Note |
|---|---|---|
| Label revision date | 2026-08-27 | |
| Label read | Mounjaro | NDA215866, brand-name application |
| Boxed warning | Yes | heading as printed: "WARNING: RISK OF THYROID C-CELL TUMORS" |
| Pregnancy section | Present | |
| Lactation section | Present | |
| Pediatric use section | Present | |
| Geriatric use section | Present |
How this was calculated
Selected the most recently revised prescription label for this single ingredient from an original manufacturer, preferring a brand-name application. Checked which sections exist and quoted headings and sentences exactly as printed.
One label: the newest prescription label for single-ingredient tirzepatide from an original manufacturer, matched to Mounjaro
Read from one label. Labels for other brands, strengths or forms of the same ingredient can differ. A missing section heading does not mean there is no guidance. Read the full label before relying on it.
At a glance
- Drug / tirzepatide (Mounjaro); approved for type 2 diabetes, not weight loss [1]
- Drug class / dual GIP and GLP-1 receptor agonist, injected once weekly
- Boxed warning / thyroid C-cell tumors in rats; human relevance unknown [1]
- Contraindicated / personal or family history of MTC or MEN 2; prior serious hypersensitivity [1]
- Gallbladder events / 0.6% vs 0% placebo in adult trials [1]
- Severe GI reactions / 1.3% (5 mg), 0.4% (10 mg), 1.2% (15 mg) vs 0.9% placebo [1]
- Biggest hypoglycemia risk / insulin or a sulfonylurea [1]
- Pancreatitis / labeled warning; label says discontinue if suspected [1]
Which serious reactions does the Mounjaro label warn about?
The warnings section of the Mounjaro label covers acute pancreatitis, hypoglycemia with insulin secretagogues or insulin, hypersensitivity reactions, acute kidney injury due to volume depletion, severe gastrointestinal reactions, diabetic retinopathy complications, acute gallbladder disease, and pulmonary aspiration during general anesthesia or deep sedation [1]. Only one of them, thyroid C-cell tumors, carries a boxed warning [1].
Most of what patients actually report is gastrointestinal and common rather than serious. In SURPASS-2, a 40-week open-label trial of 1,879 adults with type 2 diabetes on metformin, nausea was reported by 17% to 22% of tirzepatide-treated patients versus 18% with semaglutide 1 mg, diarrhea by 13% to 16% versus 12%, and vomiting by 6% to 10% versus 8% [2]. The reactions described below are the label's serious ones.
The label reports its adverse reaction data from two placebo-controlled adult trials in type 2 diabetes (SURPASS-1 and SURPASS-5), with 718 patients on Mounjaro and a mean exposure of 36.6 weeks, plus a seven-trial pool of 5,119 adults treated for a mean of 48.1 weeks; it also draws on animal findings and postmarketing reports [1]. The label states that adverse reaction rates from different trials cannot be compared directly [1].
Thyroid C-cell tumors: the boxed warning
In a 2-year study, both sexes of rats given tirzepatide developed dose-dependent and treatment-duration-dependent thyroid C-cell tumors, adenomas and carcinomas, at clinically relevant plasma exposures [1]. The label says it is unknown whether Mounjaro causes thyroid C-cell tumors, including medullary thyroid carcinoma, in humans, because the human relevance of the rodent finding has not been determined [1].
Mounjaro is contraindicated in patients with a personal or family history of medullary thyroid carcinoma or with Multiple Endocrine Neoplasia syndrome type 2 [1]. The label directs that patients be counseled about the potential MTC risk and about symptoms of thyroid tumors: a mass in the neck, dysphagia, dyspnea, or persistent hoarseness [1]. Routine serum calcitonin monitoring or thyroid ultrasound is of uncertain value for early detection, the label says, since calcitonin testing has low specificity and background thyroid disease is common [1].
Acute pancreatitis
The label warns that acute pancreatitis, including fatal and non-fatal hemorrhagic or necrotizing pancreatitis, has been observed in patients treated with GLP-1 receptor agonists or with Mounjaro [1]. Signs may include persistent or severe abdominal pain, sometimes radiating to the back, with or without nausea or vomiting [1]. The label's instruction is that if pancreatitis is suspected, Mounjaro should be discontinued and appropriate management started [1].
What people on Reddit report
Accounts from Mounjaro users: one parent describes a hospital stay with severe upper abdominal pain and vomiting, and others discuss nausea, dose timing and whether side effects are common.
The upper abdominal pain is concerning since pancreatitis/ gallbladder issues are an adverse effect of the medicine. I'd make sure they took a look for those at the hospital.Read the source discussion
She began having relentless upper abdominal pain. Three trips to the ER the last via ambulance and they finally admitted.Read the source discussion
I wouldn't say it's "common" – the side effects are remarkably specific to the individual.Read the source discussion
Gallbladder disease
Acute gallbladder disease, covering cholelithiasis, biliary colic and cholecystectomy, was reported by 0.6% of Mounjaro-treated adults and 0% of placebo-treated adults in the label's placebo-controlled trials [1]. If gallstones are suspected, the label says gallbladder studies and clinical follow-up are indicated [1].
Acute kidney injury from dehydration
The label describes postmarketing reports of acute kidney injury, in some cases requiring hemodialysis, in patients treated with GLP-1 receptor agonists or Mounjaro [1]. The majority of those events occurred in patients who had gastrointestinal adverse reactions leading to dehydration, such as nausea, vomiting or diarrhea [1]. The label says to monitor renal function in patients reporting reactions that could lead to volume depletion, especially during starting and dose escalation [1]. Separately, the label states that no dose adjustment is needed for renal or hepatic impairment [1].
Nick Sterling on how dehydration can lead to kidney injury
Nick Sterling argues that nausea and vomiting from these weight-loss injections can leave people dehydrated, and that this can progress to acute kidney injury. In his view, when plasma volume falls, the kidneys must work harder to conserve water, and emergency doctors usually spot the problem through rising creatinine and BUN levels. He also treats gastroparesis as a known side effect that is hard to separate from diabetes, and he says he has seen it in patients without diabetes who take these drugs for weight loss. His tone is clinical: these are recognizable patterns he sees arriving at emergency departments, and he wants viewers to know them.
Who is speaking?
Nick Sterling, MD, PhD. Physician with emergency department experience, as described on the channel Background
Severe gastrointestinal reactions
In placebo-controlled adult trials, severe gastrointestinal reactions were reported in 1.3% of patients on 5 mg, 0.4% on 10 mg, and 1.2% on 15 mg, compared with 0.9% on placebo [1]. Gastrointestinal adverse reactions of any severity occurred in 37.1%, 39.6% and 43.6% of patients on 5, 10 and 15 mg versus 20.4% on placebo, and treatment was discontinued for gastrointestinal reasons in 3.0%, 5.4% and 6.6% versus 0.4% [1]. Most reports of nausea, vomiting and diarrhea occurred during dose escalation and decreased over time [1]. The label states that Mounjaro is not recommended in patients with severe gastroparesis [1].
Questions worth asking
Severe hypoglycemia with insulin or a sulfonylurea
The Mounjaro label warns that hypoglycemia risk, including severe hypoglycemia, increases when the drug is used with an insulin secretagogue such as a sulfonylurea, or with insulin, and says to consider reducing the dose of the sulfonylurea or insulin when Mounjaro is started [1]. The label also tells prescribers to inform patients on those medicines about the risk and to educate them on the signs and symptoms of hypoglycemia [1].
Serious allergic reactions
The label states that serious hypersensitivity reactions, including anaphylaxis and angioedema, have been reported with Mounjaro, and that if a reaction occurs the drug should be discontinued, treated promptly per standard of care, and the patient monitored until signs and symptoms resolve [1]. A known serious hypersensitivity to tirzepatide or any excipient in Mounjaro is a contraindication [1]. The label adds caution for patients with a history of angioedema or anaphylaxis to a GLP-1 receptor agonist, since it is unknown whether they are predisposed to the same reactions with Mounjaro [1].
Diabetic retinopathy
The label warns that temporary worsening of diabetic retinopathy has been reported with rapid improvement in glucose control, and says patients with a history of diabetic retinopathy should be monitored for progression [1].
Gastric emptying and anesthesia
Mounjaro delays gastric emptying, and the label warns that pulmonary aspiration has been reported in patients receiving GLP-1 receptor agonists during elective surgery or procedures under general anesthesia or deep sedation [1]. The label instructs patients to inform healthcare providers of any planned surgeries or procedures [1].
Who should not use Mounjaro
The label's contraindications are a personal or family history of medullary thyroid carcinoma, Multiple Endocrine Neoplasia syndrome type 2, and a known serious hypersensitivity to tirzepatide or an excipient [1]. On pregnancy, the label says available human data are insufficient to assess risk, that animal reproduction studies suggest possible fetal harm, and that Mounjaro should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus [1].
Check what you know
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Frequently asked questions
What are the rare but serious side effects of Mounjaro?
Does Mounjaro cause thyroid cancer in humans?
Can Mounjaro cause pancreatitis?
Does Mounjaro cause kidney damage?
Does Mounjaro cause suicidal thoughts?
What does the Mounjaro label say about surgery and anesthesia?
Reader questions
What people actually ask
Short answers drawn from the sources this article cites.
Should severe upper abdominal pain on Mounjaro be checked for pancreatitis or gallbladder disease?
The label lists persistent or severe abdominal pain, sometimes radiating to the back, as a sign of acute pancreatitis. If pancreatitis is suspected, the label says Mounjaro should be discontinued and appropriate management started. If gallstones are suspected, the label says gallbladder studies and clinical follow-up are indicated.
Asked on Reddit: Reddit participants
Do side effects during dose increases need extra attention?
The label says most reports of nausea, vomiting and diarrhea occurred during dose escalation and decreased over time. It also says to monitor renal function in patients with reactions that could lead to volume depletion, especially during starting and dose escalation.
Asked on Reddit: Reddit participants
References
Show all 6 referencesHide references
- U.S. National Library of Medicine, DailyMed. Mounjaro injection and KwikPen (tirzepatide) prescribing information. Mounjaro injection and KwikPen (tirzepatide) label
- Frías JP, Davies MJ, Rosenstock J, Pérez Manghi FC, Fernández Landó L, Bergman BK, et al. Tirzepatide versus Semaglutide Once Weekly in Patients with Type 2 Diabetes. N Engl J Med. 2021;385(6):503-515.
- Reddit participants. Side effects (r/Mounjaro). Accessed 2026-11-11.
- Reddit participants. Absolutely horrible unacceptable side effects not worth it? (r/mounjarouk). Accessed 2026-11-11.
- Reddit participants. Are the side effects really as common as they say? (r/MounjaroMaintenance). Accessed 2026-11-11.
- Nick Sterling, MD, PhD. Ozempic in the ER: Side Effects of GLP-1 Receptor Agonists. Accessed 2026-11-11.