GLP-1 Side Effects Compared
Tirzepatide, semaglutide, and liraglutide side by side — built on primary trial data, with the one head-to-head study that actually compares them, and every figure linked to its source. No cherry-picked numbers.
The short answer
All GLP-1 medications share the same gastrointestinal side effects — nausea, diarrhea, constipation, vomiting — mostly mild-to-moderate and worst during dose escalation. You cannot rank them by comparing their separate trials. The only direct comparison, SURMOUNT-5 (NEJM 2025), found tirzepatide and semaglutide had broadly similar side effects; tirzepatide produced more weight loss (~20.2% vs ~13.7%).
Key takeaways
- The common GLP-1 side effects are the same across drugs: nausea, diarrhea, constipation, vomiting — mostly mild-to-moderate, worst during the first weeks and each dose increase.
- Cross-trial percentages (e.g. 31% vs 44% nausea) are NOT comparable — they come from different trials with different populations, doses, and definitions.
- SURMOUNT-5 (NEJM 2025), the only head-to-head RCT, found tirzepatide and semaglutide had broadly similar GI side effects; tirzepatide lost more weight (~20.2% vs ~13.7% at 72 weeks).
- No single GLP-1 is "gentlest" for everyone — a slower dose titration is the biggest lever for reducing nausea on any of them.
- Serious but rare risks (pancreatitis, gallbladder disease, a boxed warning for thyroid C-cell tumors in rodents) apply across the class — discuss your history with a prescriber.
The head-to-head: SURMOUNT-5 (the only direct comparison)
SURMOUNT-5 is the first RCT to compare the two leading GLP-1 weight-loss drugs directly: tirzepatide (Zepbound) versus semaglutide 2.4mg (Wegovy) in adults with obesity and without diabetes. At 72 weeks, tirzepatide produced ~20.2% mean body-weight reduction versus ~13.7% on semaglutide — the authoritative source for any tirzepatide-vs-semaglutide comparison, because it removes the cross-trial confounding that makes separate-trial numbers misleading.At 72 weeks the two drugs' gastrointestinal side effects were broadly similar and mostly mild-to-moderate — so the honest answer to "which has fewer side effects" is "about the same," while tirzepatide had the larger weight-loss effect.
New England Journal of Medicine 2025 (PubMed) NCT05822830 on ClinicalTrials.gov
Side-effect rates by drug — from each drug's own pivotal trial
Read these down each column, not across drugs.Each drug's numbers come from a different trial (different patients, doses, and how events were counted), so comparing 31% to 44% between drugs is not valid. For a true comparison, use the head-to-head SURMOUNT-5 result above.
Zepbound / Mounjaro (tirzepatide)
Source: SURMOUNT-1 trial · NCT04184622| Side effect | % of patients (in SURMOUNT-1) |
|---|---|
| Nausea | 31% |
| Diarrhea | 22% |
| Vomiting | 13% |
| Constipation | 12% |
| Decreased appetite | 11% |
Wegovy (semaglutide 2.4mg)
Source: STEP-1 trial · NCT03548935| Side effect | % of patients (in STEP-1) |
|---|---|
| Nausea | 44% |
| Diarrhea | 30% |
| Vomiting | 24% |
| Constipation | 24% |
| Abdominal pain | 20% |
Saxenda (liraglutide 3.0mg)
Source: SCALE trial · NCT01272219| Side effect | % of patients (in SCALE) |
|---|---|
| Nausea | 39% |
| Diarrhea | 21% |
| Constipation | 19% |
| Vomiting | 16% |
| Headache | 14% |
Which GLP-1 is easiest to tolerate?
Honestly: it depends on the person and the titration, not the brand. In the one head-to-head trial the two leading drugs were similar on side effects. What reliably reduces side effects is how you take it, not which — slower dose steps, smaller lower-fat meals, hydration, and staying at a tolerated dose rather than rushing to the top. If one drug is intolerable, prescribers often switch molecule and restart titration.
Serious risks — shared across the class
Beyond the common GI effects, GLP-1 medications carry rarer but serious risks that apply to the whole class: pancreatitis, gallbladder disease, and a boxed warning for thyroid C-cell tumors seen in rodents (relevance to humans is unknown; the drugs are contraindicated with a personal or family history of medullary thyroid carcinoma or MEN 2). These are decisions for a prescriber who knows your history — this page is general information, not medical advice.
Common questions about this medication
Which GLP-1 has the least side effects?
There is no single "gentlest" GLP-1 that holds for everyone, and comparing the raw side-effect percentages from each drug's separate trial is misleading — the trials enrolled different people, used different doses, and defined events differently. The one head-to-head trial, SURMOUNT-5 (NEJM 2025), compared tirzepatide and semaglutide directly and found broadly similar gastrointestinal side effects, mostly mild to moderate. For any GLP-1, a slower dose titration is the single biggest lever for reducing nausea.
Does tirzepatide or semaglutide have worse side effects?
In SURMOUNT-5 — the first and only randomized head-to-head trial (tirzepatide/Zepbound vs semaglutide 2.4mg/Wegovy, 72 weeks, published in the New England Journal of Medicine, 2025) — the two had broadly similar gastrointestinal side-effect profiles, mostly mild-to-moderate and most common during dose escalation. Tirzepatide produced more weight loss (about 20.2% vs 13.7%). You cannot conclude one is "gentler" by comparing their separate trials, because those numbers are not from the same study.
Why are the side-effect percentages different on other websites?
Because most sources quote each drug's number from its own separate trial (SURMOUNT-1 for tirzepatide, STEP-1 for semaglutide, SCALE for liraglutide) and then place them side by side as if they were comparable — they are not. Different trial populations, escalation schedules, and adverse-event definitions make cross-trial percentages unreliable for ranking tolerability. That is exactly why the head-to-head SURMOUNT-5 trial matters.
How do I reduce GLP-1 side effects?
The most common side effects (nausea, diarrhea, constipation) are usually worst in the first weeks and after each dose increase, then ease. Practical steps: titrate the dose slowly with your prescriber, eat smaller lower-fat meals, stay hydrated, and don't lie down right after eating. Contact your clinician for severe or persistent symptoms, signs of pancreatitis (severe abdominal pain), or dehydration. This is general information, not medical advice.
Side-effect rates are from each drug's pivotal trial as published (SURMOUNT-1, STEP-1, SCALE); the head-to-head comparison is SURMOUNT-5 (New England Journal of Medicine, 2025). Figures link to ClinicalTrials.gov and PubMed. Editorial reference, not medical advice. Reviewed 2026-07-16.