Semaglutide vs Tirzepatide Side Effects: STEP 1 vs SURMOUNT-1

You are comparing two medications, and the question on your mind is simple: which one has side effects I can actually live with?

This is a legitimate concern, and it deserves a straightforward answer. Nausea, diarrhea, and other GI side effects are real, and they happen with both medications. Here is what the FDA labels and the clinical trials actually show, what they cannot tell you, and what it means for your decision.

The GLP-1 Side Effect Profile: Shared Mechanism, Same Baseline

Semaglutide activates GLP-1 receptors. Tirzepatide activates both GIP and GLP-1 receptors. Despite that difference, both FDA labels list the same most common gastrointestinal side effects^[4][5].

Both labels also state that the medication delays gastric emptying (the rate at which food leaves your stomach)^[4][5].

The most common side effects on both labels include:

• Nausea
• Diarrhea
• Constipation
• Vomiting
• Abdominal pain
• Dyspepsia (indigestion)

Both labels say these reactions were reported most often during dose escalation^[4][5]. In STEP 1, nausea and diarrhea on semaglutide were typically transient, mild to moderate, and subsided with time^[1]. How long it takes varies from person to person.

STEP 1 vs SURMOUNT-1: Cross-Trial Comparison

The rates below come from each medication’s FDA label. The Wegovy (semaglutide) label pools three placebo-controlled weight-loss trials of the 2.4 mg dose, including the trial published as STEP 1. The Zepbound (tirzepatide) label pools two placebo-controlled weight-loss trials, including SURMOUNT-1^[4][5]. These were not head-to-head studies.

Sources: Wegovy label Table 3 and Zepbound label Table 1^[4][5]. These percentages reflect the share of trial participants who reported the side effect at any point during the trials. Both labels say most GI reactions were reported during dose escalation.

Stopping treatment because of side effects was uncommon in both pivotal trials. In STEP 1, 4.5% of people on semaglutide and 0.8% on placebo stopped treatment because of gastrointestinal events^[1]. In SURMOUNT-1, adverse events led to stopping treatment in 4.3%, 7.1%, and 6.2% of people on tirzepatide 5 mg, 10 mg, and 15 mg, compared with 2.6% on placebo^[2]. Note that the two abstracts report different measures (GI-related discontinuation vs discontinuation for any adverse event).

What does this cross-trial comparison suggest? On paper, the semaglutide 2.4 mg percentages for nausea and vomiting are higher than the tirzepatide percentages. But here is the critical caveat: both labels state that adverse reaction rates observed in one drug’s trials cannot be directly compared with rates in another drug’s trials^[4][5]. The trials enrolled different people at different sites, used different doses, and escalated on different schedules (16 weeks to reach 2.4 mg in the Wegovy trials, a 20-week escalation period in SURMOUNT-1)^[2][4]. You cannot conclude from these tables that either medication is better tolerated.

SURMOUNT-5: The Head-to-Head Reality Check

SURMOUNT-5, published in 2025, is the head-to-head trial. It randomly assigned 751 adults with obesity but without type 2 diabetes to the maximum tolerated dose of tirzepatide (10 mg or 15 mg) or semaglutide (1.7 mg or 2.4 mg) for 72 weeks^[3]. It was open-label, meaning participants and investigators knew which medication was given, and it was funded by Eli Lilly, the maker of tirzepatide^[3].

What the published abstract reports about side effects: the most common adverse events in both groups were gastrointestinal, most were mild to moderate in severity, and they occurred mainly during dose escalation^[3].

The abstract does not give side-by-side rates for nausea, vomiting, or other individual side effects. So it neither confirms nor rules out the differences seen in the label tables above, and it does not show that either medication is better or worse tolerated.

On weight, the average change at 72 weeks was -20.2% with tirzepatide and -13.7% with semaglutide^[3]. Those results describe the FDA-approved products as studied in this trial. Results vary, and trial results are not a prediction for any individual.

What Accounts for Individual Variation?

If both labels list the same common side effects, why do some people tolerate one medication much better than the other? There is no test that predicts it. Factors that can play a part include:

Genetic and metabolic factors. Some people seem more sensitive than others to slowed stomach emptying. There is no routine test that predicts this in advance.

Dose escalation speed. Both medications start at a low dose and increase in steps, and both labels describe that step-by-step escalation as a way to reduce the risk of GI side effects^[4][5]. The Wegovy label says escalation can be delayed by 4 weeks if a dose is not tolerated, and the Zepbound label says a lower maintenance dose can be considered^[4][5].

Food and hydration choices. Many people find smaller, lower-fat meals easier to tolerate. Vomiting and diarrhea can lead to dehydration, and both labels warn that dehydration can lead to kidney injury^[4][5].

Concurrent medical conditions. Both labels say the medication is not recommended for people with severe gastroparesis (severely delayed stomach emptying)^[4][5]. Other conditions and medications that affect digestion may matter too, so share your full health history and medication list with the prescriber.

Serious and Rare Side Effects: The Same Warnings on Both Labels

Both labels carry the same core warnings^[4][5]. The figures below come from each label’s weight-loss trials and, as with the common side effects, cannot be compared directly between the two drugs.

Gallbladder disease. In the Wegovy label’s weight-loss trials, gallstones (cholelithiasis) were reported by 1.6% of people on the injection vs 0.7% on placebo, and gallbladder inflammation (cholecystitis) by 0.6% vs 0.2%^[4]. In the Zepbound label’s pooled trials, gallstones were reported by 1.1% vs 1%, and cholecystitis by 0.7% vs 0.2%^[5]. Tell the prescriber about any history of gallbladder problems before starting either medication.

Pancreatitis. Both labels warn about acute pancreatitis and say to stop the medication if it is suspected^[4][5]. In the Wegovy label’s weight-loss trials, acute pancreatitis was confirmed in 4 people on Wegovy and 1 on placebo^[4]. In the Zepbound label’s pooled weight-loss trials, it was confirmed in 0.2% of people on Zepbound and 0.2% on placebo^[5]. Tell the prescriber about any history of pancreatitis.

Thyroid C-cell tumors. Both labels carry a boxed warning: the medication caused thyroid C-cell tumors in rodents, and it is unknown whether it causes these tumors, including medullary thyroid carcinoma (MTC), in humans^[4][5]. Neither medication should be used by people with a personal or family history of MTC or with Multiple Endocrine Neoplasia syndrome type 2 (MEN 2), or by people with a known serious allergy to the medication or its ingredients.

Severe gastrointestinal reactions. Both labels warn that use has been associated with GI adverse reactions, sometimes severe, and say the medication is not recommended for people with severe gastroparesis^[4][5]. In the Wegovy label’s weight-loss trials, severe GI reactions were reported by 4.1% of people on the injection vs 0.9% on placebo^[4]. The Zepbound label lists postmarketing reports of ileus, intestinal obstruction, and severe constipation^[5].

Dysesthesia (altered skin sensation). The Wegovy label lists dysesthesia, which includes tingling, burning, or sensitive skin, among its most common adverse reactions. It was reported by 2% of people on 2.4 mg vs 1% on placebo in the pooled trials, and by 22% on the 7.2 mg dose vs 6% on 2.4 mg and 0.3% on placebo in the trials of the higher dose^[4]. The Zepbound label reports dysesthesia in 0.2% to 0.4% of people on Zepbound vs 0.1% on placebo^[5].

Other warnings. Both labels also warn about kidney injury from dehydration, serious allergic reactions, low blood sugar when used with insulin or sulfonylureas, diabetic retinopathy complications in people with type 2 diabetes, and the risk of inhaling stomach contents during anesthesia or deep sedation^[4][5]. The Wegovy label also lists heart rate increase^[4]. Both labels say the medication may cause fetal harm, and the Zepbound label says it may reduce the effectiveness of birth control pills, especially for 4 weeks after starting and after each dose increase^[4][5].

The warnings are the same on both labels. The published data do not show either medication to be safer for these rare events.

Injection Site Reactions: Both Medications

Both semaglutide (Wegovy) and tirzepatide (Zepbound) are given as once-weekly injections under the skin; Wegovy also comes as a daily tablet^[4][5]. Injection site reactions are possible with both.

In the Wegovy label’s weight-loss trials, 1.4% of people on Wegovy and 1% on placebo had injection site reactions^[4]. In the Zepbound label’s pooled trials, injection site reactions were reported by 6% to 8% of people on Zepbound vs 2% on placebo^[5]. As with the other rates, these come from separate trials.

Reactions listed on the labels include:

• Redness
• Swelling or hardening of the skin
• Bruising
• Itching or pain

Both labels say to rotate injection sites with each dose^[4][5]. If a reaction is severe, spreading, or does not go away, contact the prescriber.

The Practical Reality: You Cannot Predict Individual Response

Here is what clinical evidence does not tell you: how you personally will respond to each medication.

Some people tolerate semaglutide well and struggle with tirzepatide because of nausea. Others experience the opposite. There is no blood test, genetic panel, or questionnaire that predicts this.

This is why starting at a low dose and escalating in steps matters. It gives your body time to adjust and gives the prescriber information about your individual tolerance. If you start on semaglutide and find the nausea unmanageable despite a slower pace and changes to how you eat, switching to tirzepatide is an option to discuss with the prescriber. The reverse is also true.

A few people find that neither medication is tolerable because of persistent nausea or other GI side effects. In those cases, a prescriber may discuss other options, including different medications or a different dose.

What Makes the Difference: Escalation Strategy and Tolerability

Both labels use a step-by-step dose escalation to reduce the risk of GI side effects^[4][5].

Semaglutide (Wegovy injection) starts at 0.25 mg once weekly for 4 weeks, then 0.5 mg, 1 mg, and 1.7 mg, each for 4 weeks. The recommended maintenance dose for weight reduction in adults is 2.4 mg (1.7 mg is also an option), and the label allows an increase to a maximum of 7.2 mg for people who tolerate 2.4 mg for at least 4 weeks and need more weight reduction. If a dose is not tolerated during escalation, the label says escalation can be delayed by 4 weeks^[4].

Tirzepatide (Zepbound) starts at 2.5 mg once weekly for 4 weeks, then 5 mg. The dose may be increased in 2.5 mg steps after at least 4 weeks on the current dose, to a maintenance dose of 5 mg, 10 mg, or 15 mg. If a maintenance dose is not tolerated, the label says a lower maintenance dose can be considered^[5].

Some prescribers keep people at a dose longer before increasing; that is a clinical decision. No trial cited here compared escalation strategies directly, so we cannot say how much escalation speed matters compared with the choice of medication.

These schedules come from the FDA labels for the brand-name products. Compounded semaglutide and tirzepatide are not FDA-approved, and their dosing has not been reviewed by the FDA.

Managing Side Effects: Strategies That Work for Both

If you are concerned about side effects, these are common, practical steps to discuss with the prescriber:

Eat smaller meals. Large meals can make nausea worse when the stomach is emptying slowly. Many people do better with smaller meals and stopping when they feel full.

Go easy on high-fat foods. Many people find greasy or fried foods harder to tolerate. Lean protein, vegetables, and simpler meals are often easier.

Stay hydrated. Drink fluids regularly, especially if you have vomiting or diarrhea. Both labels warn that dehydration from GI side effects can lead to kidney injury^[4][5].

Ginger and peppermint. Some people use ginger or peppermint for mild nausea. Evidence for them alongside GLP-1 medications specifically is limited, so check with the prescriber or a pharmacist before adding any supplement.

Slow escalation. Ask the prescriber about delaying a dose increase if nausea is a concern. The Wegovy label allows escalation to be delayed by 4 weeks if a dose is not tolerated, and the Zepbound label sets at least 4 weeks per step, not exactly 4^[4][5].

Time your dose. Both injections can be given at any time of day, with or without meals^[4][5]. Some people prefer a day and time that fits their routine and eating patterns.

Know when to get help. Severe stomach pain that does not go away, with or without vomiting, needs prompt medical attention; both labels say to stop the medication if pancreatitis is suspected^[4][5].

Switching Medications: When It Makes Sense

If you have given one medication time at a tolerable dose and side effects remain unmanageable, switching to the other is a reasonable option to discuss with the prescriber.

Both labels start at a low dose (0.25 mg for Wegovy, 2.5 mg for Zepbound) and increase in steps^[4][5]. Neither label gives a switching schedule, so how to handle a switch, including the starting dose, is the prescriber’s decision.

Some people who could not tolerate semaglutide find tirzepatide manageable. Others experience the opposite.

There is no way to predict this in advance. A prescriber can monitor your tolerance and adjust based on your actual experience.

Bottom Line: Side Effects Are Similar, Individual Response Varies Dramatically

Both FDA labels list the same common side effects, mostly gastrointestinal and mostly during dose escalation, and the same serious warnings. The label tables show different percentages for nausea and vomiting, but they come from separate trials and cannot be compared directly. The head-to-head SURMOUNT-5 abstract reports GI events as the most common in both groups without giving side-by-side rates.

What the data cannot predict is which medication will suit your particular body. Some people tolerate semaglutide without issue. Others struggle with nausea despite slow escalation and changes to how they eat, then switch to tirzepatide and do well. There is no reliable way to forecast this.

Here is what you can control:

• Choose a provider who will adjust the pace of dose increases if needed
• Make eating changes that ease GI symptoms (smaller meals, lean protein, good hydration)
• Give a medication time at a tolerable dose before deciding, as the prescriber advises
• Know that switching medications is an option if tolerability remains poor

The goal is not to find the medication with the fewest side effects in a clinical trial. The goal is to find the medication your body tolerates well enough for you to stay on it as prescribed. For some people, that is semaglutide. For others, it is tirzepatide. Time and careful monitoring with a licensed provider will tell you which one you tolerate better.

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Citations

[1] Wilding JPH, Batterham RL, Calanna S, et al. “Once-Weekly Semaglutide in Adults with Overweight or Obesity.” N Engl J Med. 2021;384(11):989-1002. https://pubmed.ncbi.nlm.nih.gov/33567185/

[2] Jastreboff AM, Aronne LJ, Ahmad NN, et al. “Tirzepatide Once Weekly for the Treatment of Obesity.” N Engl J Med. 2022;387(3):205-216. https://pubmed.ncbi.nlm.nih.gov/35658024/

[3] Aronne LJ, Horn DB, le Roux CW, et al. “Tirzepatide as Compared with Semaglutide for the Treatment of Obesity.” N Engl J Med. 2025;393(1):26-36. https://pubmed.ncbi.nlm.nih.gov/40353578/

[4] U.S. Food and Drug Administration. WEGOVY (semaglutide) injection and tablets, prescribing information. Revised 06/2026. https://www.accessdata.fda.gov/drugsatfda_docs/label/2026/215256s025lbl.pdf

[5] U.S. Food and Drug Administration. ZEPBOUND (tirzepatide) injection, prescribing information. Revised 08/2026. https://www.accessdata.fda.gov/drugsatfda_docs/label/2026/217806Orig1s041correctedlbl.pdf