Tirzepatide vs Semaglutide Side Effects: What Direct Comparison Shows
SURMOUNT-5 (751 adults) found mostly mild-to-moderate GI side effects in both arms; a 46,620-pair real-world study found an HR of 1.07 for serious GI events with tirzepatide vs semaglutide. Label percentages cannot be compared across drugs.
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The one direct head-to-head trial, SURMOUNT-5, reported that the most common adverse events in both treatment groups were gastrointestinal, that most were mild to moderate in severity, and that they occurred primarily during dose escalation [1]. A large real-world matched-cohort study of 46,620 pairs found a hazard ratio of 1.07 (95% CI, 0.90 to 1.26) for serious gastrointestinal events with tirzepatide versus subcutaneous semaglutide, and its authors concluded the drugs studied have similar gastrointestinal safety profiles [4].
The side effect percentages printed on the Zepbound and Wegovy labels look very different from each other, but those numbers come from separate trials with different populations and placebos, and both labels state that adverse reaction rates from one drug’s trials cannot be directly compared with another drug’s trials [2, 3]. The differences that are backed by direct comparison are narrower than the label tables suggest.
Why can’t you compare the label percentages side by side?
Both the Zepbound and Wegovy prescribing information carry the same caution: because clinical trials run under widely varying conditions, adverse reaction rates observed in one drug’s trials cannot be directly compared with rates in another drug’s trials and may not reflect what happens in practice [2, 3].
The trial populations also differed. Zepbound’s safety pool for weight reduction combined two placebo-controlled trials of 2,519 adults treated for up to 72 weeks, of whom 25% had type 2 diabetes [2]. Wegovy’s 2.4 mg safety pool combined three placebo-controlled trials of 2,116 adults treated for up to 68 weeks, of whom 19% had type 2 diabetes [3].
The drugs themselves differ in mechanism. Tirzepatide is a dual GIP and GLP-1 receptor agonist (Zepbound is approved for weight reduction and obstructive sleep apnea; Mounjaro for type 2 diabetes and cardiovascular risk reduction), while semaglutide is a GLP-1 receptor agonist [2, 3, 7].
What did the head-to-head trial find?
SURMOUNT-5 was a phase 3b, open-label trial that randomly assigned 751 adults with obesity but without type 2 diabetes in a 1:1 ratio to the maximum tolerated dose of tirzepatide (10 mg or 15 mg) or semaglutide (1.7 mg or 2.4 mg), injected subcutaneously once weekly for 72 weeks [1].
On tolerability, the trial reported that the most common adverse events in both treatment groups were gastrointestinal, and most were mild to moderate in severity and occurred primarily during dose escalation [1]. The trial’s primary endpoint was weight change, not side effects: at week 72, average weight change was -20.2% with tirzepatide versus -13.7% with semaglutide [1]. The trial was funded by Eli Lilly, tirzepatide’s manufacturer [1].
What side effects does the Zepbound label list?
Against its own placebo in the pooled weight-reduction trials, Zepbound’s label reports the following rates [2]:
| Adverse reaction | Placebo | Zepbound 5 mg | 10 mg | 15 mg |
|---|---|---|---|---|
| Nausea | 8% | 25% | 29% | 28% |
| Diarrhea | 8% | 19% | 21% | 23% |
| Vomiting | 2% | 8% | 11% | 13% |
| Constipation | 5% | 17% | 14% | 11% |
| Injection site reactions | 2% | 6% | 8% | 8% |
| Hypersensitivity reactions | 3% | 5% | 5% | 5% |
| Eructation (belching) | 1% | 4% | 5% | 5% |
| Hair loss | 1% | 5% | 4% | 5% |
Discontinuation for adverse reactions occurred in 4.8%, 6.3%, and 6.7% of patients on 5 mg, 10 mg, and 15 mg respectively, versus 3.4% on placebo [2]. The Mounjaro label lists the most common reactions (reported in at least 5% of patients) as nausea, diarrhea, decreased appetite, vomiting, constipation, dyspepsia, and abdominal pain [7].
What side effects does the Wegovy label list?
In Wegovy’s pooled 2.4 mg trials, nausea was reported by 44% of patients versus 16% on placebo [3]. Discontinuation for adverse reactions occurred in 6.8% of Wegovy patients versus 3.2% on placebo, with the leading causes being nausea (1.8%), vomiting (1.2%), and diarrhea (0.7%) [3]. The label’s most-common list also includes headache, dizziness, gastroenteritis, nasopharyngitis, and hypoglycemia in patients with type 2 diabetes [3].
These figures are each measured against that drug’s own placebo in separate trials, so the 44% nausea figure for Wegovy and the 25-29% figures for Zepbound are not a head-to-head result [2, 3].
Which causes more hair loss?
Both labels report hair loss at low single-digit rates above placebo. Zepbound reports 4-5% across doses versus 1% placebo, and the label states these reactions were associated with weight reduction; hair loss was reported by 7.1% of women versus 0.5% of men taking Zepbound, and no Zepbound-treated patient stopped the drug because of hair loss [2]. Wegovy 2.4 mg reports hair loss in 3% of patients versus 1% on placebo [3]. These come from separate trials, so they cannot be ranked against each other [2, 3].
What about injection site reactions and antibodies with tirzepatide?
Anti-tirzepatide antibodies were detected in 64.5% (1,591 of 2,467) of Zepbound-treated patients in the weight-reduction studies [2]. Injection site reactions occurred in 11.3% of patients who developed these antibodies versus 1% of those who did not, and hypersensitivity reactions occurred in 6.2% with antibodies versus 3% without, mostly skin reactions such as rash and itching [2]. The label states that no clinically significant effect of anti-tirzepatide antibodies on pharmacokinetics or effectiveness has been identified [2].
A 2026 FAERS pharmacovigilance study of 123,145 tirzepatide reports from Q2 2022 through Q4 2025 found that injection-site reactions and medication errors were the strongest signals [8].
Do serious gut events differ in the real world?
A 2025 Annals of Internal Medicine cohort study matched adults with type 2 diabetes who started dulaglutide, subcutaneous semaglutide, or tirzepatide between January 1, 2019 and August 30, 2024, using 1:1 propensity matching [4]. The outcome was a composite of acute pancreatitis, biliary disease, bowel obstruction, gastroparesis, and severe constipation [4].
In the 46,620 matched pairs of tirzepatide versus subcutaneous semaglutide, the hazard ratio was 1.07 (95% CI, 0.90 to 1.26) [4]. Against dulaglutide, the hazard ratios were 0.96 (0.87 to 1.06) for semaglutide and 0.96 (0.77 to 1.20) for tirzepatide, and the authors concluded that the three drugs have similar gastrointestinal safety profiles in adults with type 2 diabetes [4].
What do FDA adverse event reports show?
The same 2026 FAERS study found that, compared with semaglutide, tirzepatide showed lower reporting odds for vomiting, constipation, and decreased appetite [8]. Among reports with valid onset data, the median time to onset was 13 days, with 67.1% of events occurring within 30 days of starting [8]. The study also flagged novel unlabeled signals including eructation, hunger, food craving, and starvation ketoacidosis [8].
FAERS is a voluntary reporting system, and the NANOS/AAO consensus statement notes that such data carry confounding, selection bias, under-reporting, and publicity-driven reporting [6].
Does tirzepatide carry the same NAION eye signal as semaglutide?
NAION (non-arteritic anterior ischemic optic neuropathy) is a rare condition with an annual incidence of 2.3 to 10.2 per 100,000 people; it causes sudden painless vision loss that is often permanent, and there is no known effective treatment [6].
A 2026 FAERS analysis using the MedDRA term “optic ischaemic neuropathy” through Q3 2025 found 355 reports for semaglutide with a reporting odds ratio of 94.45 (95% CI, 83.02-107.45), and 49 reports for tirzepatide with a reporting odds ratio of 2.94 (95% CI, 2.20-3.93); liraglutide had 13 reports (ROR 4.58), and no signal was identified for dulaglutide, exenatide, or lixisenatide [5]. These are reporting disproportionality measures, not measures of risk or incidence [5, 6]. The authors noted that the absence of signals for other GLP-1 drugs argues against a uniform class effect, and that causality requires prospective studies with confirmed diagnoses [5].
An earlier FAERS/VigiBase pharmacovigilance study found an association for semaglutide but no association for tirzepatide [6].
A NANOS and American Academy of Ophthalmology consensus statement from May 2026 concluded there is a possible association between semaglutide and NAION, that if present the risk elevation is likely in the range of about 2-fold, and that causality has not been established [6]. It noted that other GLP-1 drugs, particularly tirzepatide, have been less studied, and that one should not assume the risk is specific to semaglutide [6]. A TriNetX study that pooled semaglutide and tirzepatide (about 80,000 patients per group) found NAION in 0.04% of the GLP-1 group versus 0.02% of controls, HR 1.76 (95% CI, 1.01-3.07) [6]. In June 2025 the EMA recommended adding NAION as a “very rare” side effect to semaglutide product information and recommended immediately stopping semaglutide in the setting of a confirmed NAION diagnosis; NANOS and the Academy do not support that stop recommendation [6]. For sudden vision loss while on a GLP-1, NANOS and the Academy recommend immediate evaluation by an ophthalmologist [6].
How do the labels differ on warnings?
The Zepbound and Mounjaro labels advise females using oral contraceptives to switch to a non-oral method or add a barrier method for 4 weeks after starting and for 4 weeks after each dose increase [2, 7]. This is because a single 5 mg tirzepatide dose reduced the maximum concentration of oral contraceptive hormones by 59%, 66%, and 55% and overall exposure by 20%, 21%, and 23% [2].
The Wegovy label carries a Heart Rate Increase warning (section 5.9), while the Zepbound warnings list (5.1 through 5.10) has no heart rate item [2, 3].
Most warnings are shared: the rodent thyroid C-cell boxed warning, contraindication with MTC or MEN 2, pancreatitis, gallbladder disease, kidney injury from volume depletion, severe gastrointestinal reactions, hypersensitivity, hypoglycemia risk with insulin or secretagogues, diabetic retinopathy complications, and aspiration during anesthesia [2, 3]. The suicidal behavior and ideation warning was removed in February 2026 from both Zepbound and Wegovy [2, 3].
What about longer-term safety data for tirzepatide?
SURPASS-CVOT randomized 13,299 patients with type 2 diabetes and atherosclerotic cardiovascular disease to tirzepatide (up to 15 mg) or dulaglutide (1.5 mg) in a double-blind design [9]. Primary cardiovascular events occurred in 12.2% versus 13.1% (HR 0.92, 95% CI, 0.83 to 1.01), meeting noninferiority [9]. Adverse events appeared similar overall, though more gastrointestinal events were observed with tirzepatide [9]. The comparator was dulaglutide, not semaglutide, so this trial does not directly compare the two drugs [9].
What are the limits of this evidence?
SURMOUNT-5 is one open-label trial of 751 people without diabetes, funded by the maker of tirzepatide, with weight as its primary endpoint [1]. The Annals cohort covered only adults with type 2 diabetes and a composite of severe gastrointestinal events [4]. FAERS reporting odds ratios measure reporting patterns, not incidence [5, 6].
Sources
- New England Journal of Medicine. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity.
- DailyMed. ZEPBOUND (tirzepatide) injection, solution.
- US Food and Drug Administration. WEGOVY (semaglutide) prescribing information. 2026.
- PubMed. Comparative Gastrointestinal Safety of Dulaglutide, Semaglutide, and Tirzepatide in Adults With Type 2 Diabetes.
- Diabetes, Obesity and Metabolism. Optic Ischaemic Neuropathy in Incretin-Based Therapy: A Comparative Analysis of Real-World Safety Data. 2026.
- American Academy of Ophthalmology. Glucagon-Like Peptide-1 Receptor Agonists and the Risk of Non-Arteritic Anterior Ischemic Optic Neuropathy: A Consensus Statement by NANOS and the American Academy of Ophthalmology.
- DailyMed. MOUNJARO (tirzepatide) injection, solution.
- PubMed. Safety Profile of Tirzepatide in Real-World Clinical Practice: A Pharmacovigilance Study Using the FAERS Database.
- New England Journal of Medicine. Cardiovascular Outcomes with Tirzepatide versus Dulaglutide in Type 2 Diabetes.
Frequently asked questions
Which causes more nausea and vomiting, Zepbound or Wegovy?
SURMOUNT-5 reported gastrointestinal events as the most common adverse events in both arms, mostly mild to moderate. The Zepbound label reports nausea of 25-29% across doses versus 8% placebo, and Wegovy reports 44% versus 16% placebo, but each figure is against its own placebo in different trials, and both labels state such rates cannot be directly compared across drugs [2, 3].
Is tirzepatide easier to tolerate than semaglutide?
SURMOUNT-5 reported gastrointestinal events as most common in both arms, mostly mild to moderate and mainly during dose escalation. A matched cohort of 46,620 pairs found an HR of 1.07 (95% CI, 0.90-1.26) for serious GI events with tirzepatide versus subcutaneous semaglutide. FAERS data show lower reporting odds for vomiting, constipation, and decreased appetite with tirzepatide, but that measures reporting, not incidence.
How do Mounjaro and Ozempic side effects compare?
The Mounjaro label lists nausea, diarrhea, decreased appetite, vomiting, constipation, dyspepsia, and abdominal pain as its most common reactions, reported in at least 5% of patients. In a matched cohort of adults with type 2 diabetes, tirzepatide and subcutaneous semaglutide showed similar serious gastrointestinal safety profiles, with an HR of 1.07 (95% CI, 0.90-1.26).
Which drug causes more hair loss?
Both labels report low rates above placebo: 4-5% for Zepbound versus 1% placebo, and 3% for Wegovy 2.4 mg versus 1% placebo [2, 3]. Zepbound hair loss was linked to weight reduction, occurred in 7.1% of women versus 0.5% of men, and no Zepbound patient stopped for it. These come from separate trials and cannot be ranked against each other [2, 3].
Does tirzepatide affect birth control pills?
Yes. A single 5 mg tirzepatide dose reduced oral contraceptive hormone maximum concentrations by 59%, 66%, and 55% and exposure by 20%, 21%, and 23%. The Zepbound and Mounjaro labels advise switching to a non-oral method or adding a barrier method for 4 weeks after starting and after each dose increase [2, 7].
Does tirzepatide carry the same NAION eye risk as semaglutide?
The evidence is mixed and based on reporting patterns, not proven risk. One FAERS analysis found a strong semaglutide signal (ROR 94.45) and a smaller tirzepatide signal (ROR 2.94) for "optic ischaemic neuropathy" reports. An earlier FAERS/VigiBase study found no tirzepatide association. NANOS/AAO say causality is unestablished and one should not assume the risk is specific to semaglutide.
When do side effects usually start?
Early. In SURMOUNT-5, the most common adverse events were gastrointestinal, mostly mild to moderate, and occurred primarily during dose escalation. In FAERS tirzepatide reports with onset data, the median time to onset was 13 days, and 67.1% of events occurred within 30 days of starting.
What about injection site reactions with tirzepatide?
Anti-tirzepatide antibodies were detected in 64.5% of Zepbound-treated patients in the weight studies, and injection site reactions occurred in 11.3% of those with antibodies versus 1% without. The label states no clinically significant antibody effect on pharmacokinetics or effectiveness has been identified. FAERS data also show injection-site reactions among tirzepatide's strongest signals.
This article summarizes FDA labeling, published research and company information current as of September 14, 2026. It is not medical advice and does not replace a conversation with your own healthcare provider. How we research and verify.