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The most common tirzepatide side effects are digestive: nausea, diarrhea, vomiting, constipation, stomach pain and indigestion. According to the U.S. prescribing information for Mounjaro and Zepbound, both revised in August 2026, these effects happen mostly while the dose is being increased and tend to ease over time. Less common but more serious risks include pancreatitis, gallbladder disease, kidney injury from dehydration, serious allergic reactions and a boxed warning about thyroid C-cell tumors. This guide summarizes what both labels say, with the percentages reported in their clinical trials.
Peptide Labs does not sell tirzepatide or any prescription drug. This article is general information, not medical advice. If you take tirzepatide and have symptoms, contact your prescriber or pharmacist.
Key Takeaways
- Nausea affected 25% to 29% of adults in Zepbound's weight-management trials, versus 8% on placebo.
- Most nausea, vomiting and diarrhea happened during dose increases and decreased over time.
- Both labels carry a boxed warning about thyroid C-cell tumors seen in rats.
- Tirzepatide can make birth control pills less effective after starting and after each dose increase.
- The FDA had the suicidal-thoughts warning removed from Zepbound's label in early 2026.
Most common tirzepatide side effects
Tirzepatide is sold as Mounjaro for type 2 diabetes and as Zepbound for weight management and obstructive sleep apnea in adults with obesity. The two labels report side effects from different trial populations, so their numbers differ. The table shows the percentages in the placebo group and the range across the three maintenance-dose groups in each label’s main table.
| Side effect | Zepbound trials: placebo | Zepbound trials: tirzepatide | Mounjaro trials: placebo | Mounjaro trials: tirzepatide |
|---|---|---|---|---|
| Nausea | 8% | 25-29% | 4% | 12-18% |
| Diarrhea | 8% | 19-23% | 9% | 12-17% |
| Vomiting | 2% | 8-13% | 2% | 5-9% |
| Constipation | 5% | 11-17% | 1% | 6-7% |
| Stomach (abdominal) pain | 5% | 9-10% | 4% | 5-6% |
| Indigestion (dyspepsia) | 4% | 9-10% | 3% | 5-8% |
| Decreased appetite | Not listed | Not listed | 1% | 5-11% |
| Injection site reactions | 2% | 6-8% | Not listed | Not listed |
| Fatigue | 3% | 5-7% | Not listed | Not listed |
| Allergic (hypersensitivity) reactions | 3% | 5% | Not listed | Not listed |
| Belching | 1% | 4-5% | Under 1% | 3% or less |
| Hair loss | 1% | 4-5% | Not listed | Not listed |
| Heartburn (GERD) | 2% | 4-5% | Under 1% | 3% or less |
“Not listed” means the reaction did not appear in that label’s main table. The Zepbound figures come from two 72-week trials in 2,519 adults with obesity or overweight; the Mounjaro figures come from two diabetes trials with an average exposure of about 37 weeks. Rates from different trials cannot be compared directly. Hair loss in the Zepbound trials was linked to weight reduction and was reported more often in women (7.1%) than men (0.5%).
When digestive side effects tend to happen
Both labels say the majority of nausea, vomiting and diarrhea occurred during dose escalation and decreased over time. That is why treatment starts at a low dose that a prescriber raises in steps no more often than every four weeks. In the Zepbound weight trials, 56% of people on tirzepatide reported digestive side effects versus 30% on placebo, and 1.9% to 4.3% stopped treatment because of them, versus 0.5% on placebo. Overall, 4.8% to 6.7% stopped Zepbound because of any side effect, versus 3.4% on placebo, mostly in the first few months.
The Medication Guide advises drinking fluids to lower the chance of dehydration and telling a healthcare provider about stomach problems that are severe or do not go away.
Serious side effects and label warnings
Boxed warning: thyroid C-cell tumors
Tirzepatide caused thyroid C-cell tumors in rats. It is unknown whether it causes these tumors, including medullary thyroid carcinoma, in humans. Tirzepatide should not be used by people with a personal or family history of medullary thyroid carcinoma or with Multiple Endocrine Neoplasia syndrome type 2.
Other warnings on both labels
- Pancreatitis. In the Zepbound weight trials, adjudicated acute pancreatitis occurred in 0.2% of both groups. After approval, hemorrhagic and necrotizing pancreatitis, sometimes fatal, has been reported.
- Gallbladder disease. Gallstones were reported in 1.1% on Zepbound and 1% on placebo, and gallbladder inflammation in 0.7% versus 0.2%.
- Low blood sugar. The risk rises when tirzepatide is combined with insulin or a sulfonylurea. In a Zepbound trial of adults with type 2 diabetes, 4.2% had low blood sugar versus 1.3% on placebo.
- Kidney injury from dehydration. Acute kidney injury was reported in 0.5% on Zepbound and 0.2% on placebo; post-approval reports include kidney failure sometimes needing dialysis.
- Severe digestive reactions. Tirzepatide is not recommended for people with severe gastroparesis.
- Serious allergic reactions. Anaphylaxis and angioedema have been reported. Reactions within a day of an injection occurred in 2.1% on Zepbound versus 0.4% on placebo.
- Diabetic retinopathy. People with type 2 diabetes and a history of diabetic eye disease should be monitored; both labels updated this section in August 2026.
- Anesthesia. Because tirzepatide slows stomach emptying, there have been reports of stomach contents entering the lungs during surgery or deep sedation, so patients are told to inform their care team beforehand.
- Shared pens. A KwikPen must never be shared between people, even with a new needle.
What happened to the suicidal-thoughts warning?
Zepbound’s label used to include a warning to monitor for depression and suicidal thoughts, a precaution applied to weight-management drugs. On January 13, 2026, the FDA asked for that warning to be removed from Zepbound, Wegovy and Saxenda after a review, including a meta-analysis of 91 placebo-controlled trials and a study of more than 2.2 million new users, found no increased risk. Zepbound’s label recorded the removal in February 2026. Mounjaro, as a diabetes drug, never had the warning. The FDA still advises telling a healthcare professional about new or worsening depression, suicidal thoughts or unusual mood changes.
Birth control, other medicines and pregnancy
Tirzepatide can make oral hormonal contraceptives less effective. Both labels advise people who use birth control pills to switch to a non-oral method, or add a barrier method, for 4 weeks after starting tirzepatide and for 4 weeks after each dose increase. Contraceptives that are not taken by mouth are not expected to be affected. Because tirzepatide slows stomach emptying, it can change how other oral medicines are absorbed, and the Zepbound label names warfarin as an example that needs monitoring. Based on animal studies, tirzepatide may cause fetal harm, and the Zepbound label says to stop it when pregnancy is recognized.
What the labels tell patients to report
The Medication Guide lists symptoms that need prompt attention:
- A lump or swelling in the neck, hoarseness, trouble swallowing or shortness of breath.
- Severe stomach pain that will not go away, with or without vomiting, sometimes felt in the back: stop tirzepatide and call a provider right away.
- Upper stomach pain, fever, yellowing of the skin or eyes, or clay-colored stools.
- Swelling of the face, lips, tongue or throat, trouble breathing, severe rash, fainting or a very fast heartbeat: get medical help right away.
- Nausea, vomiting or diarrhea that does not go away, which can lead to dehydration.
- Changes in vision, for people with type 2 diabetes.
- Any planned surgery or procedure involving anesthesia or deep sedation.
Recent label changes, 2025-2026
Both labels changed several times in the past year. Mounjaro added use in children 10 and older with type 2 diabetes in December 2025 and an indication to lower the risk of major cardiovascular events in adults with type 2 diabetes at high risk in August 2026. Both labels updated the severe digestive reactions section, added multi-dose KwikPen instructions in January 2026 and revised the diabetic retinopathy section in August 2026. For how these safety profiles compare with semaglutide, see semaglutide side effects and semaglutide vs tirzepatide. Our tirzepatide profile covers the drug itself, and retatrutide, a related investigational drug, has no approved label yet.
Frequently Asked Questions
What are the most common side effects of tirzepatide?
Nausea, diarrhea, vomiting, constipation, stomach pain and indigestion. In Zepbound’s weight trials, nausea affected 25% to 29% of adults on tirzepatide versus 8% on placebo.
How long do tirzepatide side effects last?
Both labels say most nausea, vomiting and diarrhea occurred during dose increases and decreased over time. Symptoms that are severe or do not go away should be reported to a healthcare provider.
Does tirzepatide cause hair loss?
Hair loss was reported in 4% to 5% of adults on Zepbound versus 1% on placebo, more often in women. The label links it to weight reduction.
Does tirzepatide affect birth control?
Yes. It can make birth control pills less effective. The labels advise switching to a non-oral method or adding a barrier method for 4 weeks after starting and after each dose increase.
Is there a suicide warning on Zepbound?
Not anymore. The FDA asked for the warning to be removed in January 2026 after finding no increased risk, and the label was updated in February 2026. The FDA still advises reporting mood changes.
Are Mounjaro and Zepbound side effects the same?
They contain the same drug and share the same warnings, but their labels report different percentages because the trials enrolled different people for different lengths of time.
This article is general information, not medical advice. Peptide Labs does not sell prescription drugs, including any product named here. Read the Medication Guide that comes with a prescription, and ask a pharmacist or prescriber how this information applies to you.
Last reviewed September 2026.
Related guides: Zepbound Side Effects: What the Latest Zepbound Label Reports, Mounjaro vs Zepbound: Same Tirzepatide, Different Approvals, Retatrutide Side Effects: What the Trials Have Reported, GLP-1 Side Effects: What Every GLP-1 Drug Label Warns About, Zepbound and Alcohol: What GLP-1 Labels and Research Say.