Tirzepatide side effects: what the trials show

Complete guide: GLP-1 drugs: a complete guide to semaglutide and beyond

What are the side effects of tirzepatide?

Tirzepatide (marketed as Mounjaro and Zepbound) is a peptide that activates the GIP and GLP-1 receptors¹. Its most common adverse effects are gastrointestinal: nausea, diarrhea, vomiting, constipation, abdominal pain and dyspepsia. In the US label (revised August 2026), the table of adult placebo-controlled trials shows nausea in 12%, 15% and 18% at 5, 10 and 15 mg versus 4% with placebo; diarrhea in 12, 13 and 17% versus 9%; and vomiting in 5, 5 and 9% versus 2%¹. Injection-site reactions were 3.2% versus 0.4% with placebo¹.

A meta-analysis of trials in people with obesity without diabetes found gastrointestinal events were 1.86 times more frequent with semaglutide and tirzepatide than with placebo; the relative risk was 2.94 (95% CI 2.61–3.32) for tirzepatide and 1.68 (1.46–1.94) for semaglutide, with mostly mild cases⁶. Those figures describe trial doses and populations, not use outside them.

Nausea, vomiting and diarrhea: when they appear and how long they last

In SURMOUNT-1 (72 weeks, obesity), the most common events were gastrointestinal, mostly mild to moderate and concentrated in the dose-escalation phase⁴. Adverse events led to discontinuation in 4.3%, 7.1% and 6.2% at 5, 10 and 15 mg, and in 2.6% with placebo⁴. In SURMOUNT-2, in people with obesity and type 2 diabetes, the most frequent events were also gastrointestinal, with fewer than 5% discontinuations⁵.

Against semaglutide 1 mg (SURPASS-2, 40 weeks), nausea was 17–22% with tirzepatide and 18% with semaglutide; diarrhea, 13–16% versus 12%; and vomiting, 6–10% versus 8%. Serious adverse events were 5–7% with tirzepatide and 3% with semaglutide³. The label states that gastrointestinal reactions can be severe and that the drug is not recommended in severe gastroparesis¹.

Dehydration and kidney risk

Severe vomiting and diarrhea can cause volume depletion. The label therefore carries a warning of acute kidney injury due to volume depletion and asks for renal monitoring in patients with reactions that could lead to it¹. The manufacturer's medical information adds postmarketing reports of acute kidney injury, in some cases requiring hemodialysis².

Tirzepatide and pancreatitis: what the data say

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 tirzepatide, and says to discontinue the drug if it is suspected¹. Trials, however, show very infrequent events. A meta-analysis of nine trials with 9,871 participants found no significant increase (RR 1.46; 95% CI 0.59–3.61)⁷. Another, with 19 trials and 15,471 participants, estimated incidence at 0.22% and found no differences among 5, 10 and 15 mg (15 mg versus 5 mg: RR 0.70; 0.27–1.82)⁸. In the 21-trial, 99,599-patient meta-analysis of GLP-1 receptor agonists, pancreatitis did not differ from controls⁹.

The figures should be read with caution: the authors of the dose-response analysis note that all trials were industry-funded, follow-up was short to moderate and precision is limited⁸.

Gallbladder and gallstones: the most consistent signal

The label includes a warning of acute gallbladder disease (cholelithiasis, cholecystitis) reported in GLP-1 receptor agonist trials and in postmarketing use¹. In the nine-trial meta-analysis, the composite of gallbladder or biliary disease was associated with tirzepatide versus placebo or basal insulin (RR 1.97; 95% CI 1.14–3.42), although cholelithiasis, cholecystitis or biliary disease individually were not⁷. In the analysis of people with obesity, semaglutide increased gallbladder disorders (cholelithiasis, RR 2.6) while tirzepatide showed no significant biliary risk⁶. And in the class-wide cardiovascular meta-analysis, gallbladder disorders rose 26% and gastrointestinal disorders 63%⁹. The readings differ because population, dose and definitions differ; the prudent conclusion is that the gallbladder deserves attention, especially during rapid weight loss.

Other adverse effects worth knowing

• Hypoglycemia: uncommon as monotherapy (1% with placebo and 0% with tirzepatide), but with basal insulin the label reports 14–19% with tirzepatide versus 13% with placebo, with severe hypoglycemia up to 2%¹. In SURPASS-2, 0.2–1.7% with tirzepatide³.
• Anesthesia and sedation: delayed gastric emptying is in the label¹. A meta-analysis of observational studies found no association with pulmonary aspiration (OR 1.04; 0.87–1.25) but more residual gastric contents despite fasting (OR 5.96; 3.96–8.98)¹⁰. The AGA published a rapid practice update for management before endoscopy¹¹. More in perioperative aspiration with GLP-1.
• Hypersensitivity and diabetic retinopathy: the label mentions serious hypersensitivity reactions and temporary worsening of diabetic retinopathy with rapid glucose improvement¹. A semaglutide meta-analysis found an OR of 3.92 (1.02–15.02) for non-arteritic anterior ischemic optic neuropathy, with evidence still insufficient for definitive conclusions; the same has not been shown for tirzepatide¹⁴.
• Thyroid: the boxed warning on C-cell tumors rests on rodent data¹. A Scandinavian study of 145,410 GLP-1 receptor agonist users found an HR of 0.93 (0.66–1.31)¹². More in GLP-1 and thyroid cancer.
• Oral contraceptives: a pharmacokinetic review notes changes in oral contraceptive exposure after tirzepatide and the need for monitoring¹³.

How they compare with other GLP-1 receptor agonists

The profile is a class profile: GLP-1 receptor agonists as a group increased digestive and gallbladder events but reduced all-cause mortality (IRR 0.88; 95% CI 0.84–0.92) and major cardiovascular events (0.87) across 21 trials with 99,599 patients⁹. That balance depends on who receives them; the trials included high-risk populations. For the mechanism and trial design, see tirzepatide mechanism.