Drug facts
Liraglutide vs tirzepatide: Saxenda and Zepbound
Quick answer
No trial has compared them for weight loss. Each was tested against placebo in its own trials: weight fell 15.0% to 20.9% over 72 weeks on Zepbound (tirzepatide) against 3.1% on placebo, and 7.4% over 56 weeks on Saxenda (liraglutide) against 3%. Different trials, different lengths, different people: side by side, not head to head. What the labels do settle directly is the schedule. Saxenda is injected every day; Zepbound once a week.
There is no head-to-head trial1
A search of PubMed and of ClinicalTrials.gov in September 2026 found no randomized trial designed to compare liraglutide with tirzepatide as weight-loss treatments. The comparison the two names invite has not been run.
One randomized study does include both drugs, and it is worth knowing what it is and is not.2 A six-week phase 1 trial of 114 adults, published in Nature Medicine in 2025, randomized participants to blinded tirzepatide or placebo, or to open-label daily liraglutide. Its primary outcome was how much people ate at a test lunch after three weeks, comparing tirzepatide with placebo. Liraglutide was a reference arm, not the comparison the trial was built to test, and the published abstract reports no tirzepatide-versus-liraglutide result.
Both labels warn against the shortcut this page is tempting you toward. Section 6.1 of each says, in almost the same words, that because trials run under widely varying conditions, “adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug.” That is the Zepbound wording; Saxenda’s differs by one word. Everything below is two sets of numbers from two different programs, set next to each other.
What the two labels say, side by side3
This part is a straight comparison, because it is what each approved label states about its own product.
| Saxenda (liraglutide) | Zepbound (tirzepatide) | |
|---|---|---|
| What it is | GLP-1 receptor agonist | GIP receptor and GLP-1 receptor agonist |
| How often | Once daily, any time of day, without regard to meals | Once weekly, any time of day, with or without meals |
| Escalation | 0.6 mg a day for a week, then up weekly to 3 mg a day from week 5 | 2.5 mg for 4 weeks, then 2.5 mg steps at least 4 weeks apart |
| Maintenance | 3 mg daily for adults; lower doses are for titration only | 5, 10 or 15 mg weekly for weight; 10 or 15 mg for sleep apnea |
| Approved for | Adults with obesity, or overweight with a weight-related condition; children 12 and older over 60 kg with obesity | Adults with obesity, or overweight with a weight-related condition; moderate to severe sleep apnea in adults with obesity |
| Comes as | Prefilled 3 mL pen, 6 mg/mL | Single-dose pen, single-dose vial, multi-dose vial, KwikPen |
| A missed dose | Resume with the next daily dose; if more than 3 days have passed, restart at 0.6 mg and re-escalate | Take within 4 days; after that, skip it and keep the usual day |
| Boxed warning | Thyroid C-cell tumors | Thyroid C-cell tumors |
Both are used, in their labels’ words, in combination with a reduced-calorie diet and increased physical activity, and both delay gastric emptying.4 The Zepbound schedule is unpacked in dosage and titration, and what the second receptor adds in how tirzepatide works.
The weight trials, side by side, not head to head4
Each label’s Study 1 is the closest match the two programs offer: adults with obesity, or overweight with a related condition, and no type 2 diabetes. For Zepbound that trial is SURMOUNT-1; for Saxenda, it matches the published SCALE Obesity and Prediabetes trial.5 The figures below are each label’s own.
| Saxenda, Study 1 (SCALE) | Zepbound, Study 1 (SURMOUNT-1) | |
|---|---|---|
| Length | 56 weeks, titrated over 4 | 72 weeks, escalation up to 20 |
| Enrolled | 3,731, randomized 2:1 | 2,539, randomized 1:1:1:1 |
| Mean BMI | 38.3 | 38 |
| Women | 79% | 68% |
| Weight change on drug | −7.4% (3 mg daily) | −15.0%, −19.5%, −20.9% (5, 10, 15 mg) |
| Weight change on placebo | −3% | −3.1% |
| Lost at least 5% | 62.3% vs 34.4% on placebo | 85.1% to 90.9% vs 34.5% on placebo |
| Lost 10% or more | 33.9% vs 15.4% (label: more than 10%) | 68.5% to 83.5% vs 18.8% |
Two things line up and several do not. Both trials gave every participant, placebo included, instruction on a diet about 500 kcal a day below need and counseling toward at least 150 minutes of activity a week, and the two placebo groups lost almost the same, 3% and 3.1%. But Zepbound’s trial ran 16 weeks longer, enrolled a different mix of people, and handled missing data by a different method. The drugs have never been given to the same people under the same protocol.
The diabetes trials tell the same story at lower numbers. In each label’s Study 2, adults with type 2 diabetes lost 5.4% on Saxenda against 1.7% on placebo over 56 weeks, and 12.8% and 14.7% on Zepbound 10 and 15 mg against 3.2% over 72 weeks.
If you have seen different SCALE figures elsewhere, that is why the source matters. The published SCALE abstract reports 63.2% against 27.1% losing at least 5%, and a mean loss of 8.4 kg against 2.8 kg, using a different way of filling in missing data from the one behind the label’s table.5 The SURMOUNT-1 abstract, likewise, rounds the label’s figures to 85%, 89% and 91%.6 SURMOUNT-1 in full →
Side effects: each label’s own table3
The same warning applies twice over here, since the labels count reactions in different trial pools. Read each column against its own placebo, not against the other drug.
| Reaction | Saxenda | Its placebo | Zepbound | Its placebo |
|---|---|---|---|---|
| Nausea | 39.3% | 13.8% | 25–29% | 8% |
| Diarrhea | 20.9% | 9.9% | 19–23% | 8% |
| Constipation | 19.4% | 8.5% | 11–17% | 5% |
| Vomiting | 15.7% | 3.9% | 8–13% | 2% |
| Headache | 13.6% | 12.6% | Not listed | — |
| Dyspepsia | 9.6% | 2.7% | 9–10% | 4% |
In Saxenda’s adult trials, 9.8% stopped for an adverse reaction against 4.3% on placebo; in Zepbound’s pooled trials, 4.8% to 6.7% against 3.4%. Severe gastrointestinal reactions were reported in 4.8% on Saxenda against 1.4%, and in 1.7% to 3.1% on Zepbound against 1%. The serious warnings are largely shared: pancreatitis, gallbladder disease, kidney injury from dehydration, severe gastrointestinal reactions and aspiration under anesthesia appear on both. Saxenda’s label also gives heart rate increase a warning of its own. Zepbound’s reactions are covered one by one in side effects, and the headache difference in tirzepatide and headaches.
Taking them together, or switching4
Both labels rule out combining them. Zepbound’s limitation of use says coadministration “with any glucagon-like peptide-1 (GLP-1) receptor agonist is not recommended,” and liraglutide is one; Saxenda’s says the same of any other GLP-1 receptor agonist.
Neither label says how to move from one to the other. The Zepbound label never mentions liraglutide or Saxenda, and the Saxenda label never mentions tirzepatide or Zepbound, so there is no conversion and no transition schedule in either. That is the prescriber’s call. What changes when you switch →
Where compounded sits
On the label — Mounjaro / Zepbound
Every figure on this page describes an approved product in its own controlled trials. Even between the two approved drugs, the comparison is cross-trial.
In a compounded vial
No trial has measured a compounded tirzepatide vial against anything, including placebo. Concentration and excipients differ between compounders. What that means for whether it works →
A head-to-head does exist against a different drug. In SURMOUNT-5, tirzepatide was tested directly against semaglutide. At week 72 weight fell by 20.2% on tirzepatide and 13.7% on semaglutide. Waist circumference fell by 18.4 cm and 13.0 cm respectively. Tirzepatide vs semaglutide →
Nothing here is medical advice or a recommendation of either drug. Which one suits a particular person, and how to change between them, is for the prescriber. See the medical disclaimer.
Questions
- Is tirzepatide better than liraglutide for weight loss?
- No trial has tested that directly. In their own placebo-controlled trials, weight fell 15.0% to 20.9% over 72 weeks on Zepbound (tirzepatide) and 7.4% over 56 weeks on Saxenda (liraglutide). Those are different trials with different lengths and participants, so the gap between them is not a measured difference between the drugs.
- What is the difference between Saxenda and Zepbound?
- Saxenda is liraglutide, a GLP-1 receptor agonist injected once a day, working up to 3 mg over four weeks. Zepbound is tirzepatide, a GIP and GLP-1 receptor agonist injected once a week, starting at 2.5 mg and rising in 2.5 mg steps at least four weeks apart to a maintenance dose of 5, 10 or 15 mg. Saxenda is also approved for some children 12 and older; Zepbound is approved only for adults, and additionally for obstructive sleep apnea.
- Can Saxenda and Zepbound be used together?
- Both labels say no. Zepbound's label says coadministration with any GLP-1 receptor agonist is not recommended, and Saxenda's says the same about any other GLP-1 receptor agonist.
- How do you switch from Saxenda to Zepbound?
- Neither label says. The Zepbound label does not mention liraglutide or Saxenda, and the Saxenda label does not mention tirzepatide or Zepbound, so neither gives a switching schedule or a dose conversion. That decision belongs to the prescriber.
Sources
- PubMed, searched through the NCBI E-utilities esearch endpoint, and ClinicalTrials.gov, searched for studies of tirzepatide and liraglutide together, September 2026 PubMed
- Martin CK, Carmichael OT, Carnell S, et al. Tirzepatide on ingestive behavior in adults with overweight or obesity: a randomized 6-week phase 1 trial. Nat Med. 2025 Sep;31(9):3141-3150. PMID 40555748, verified through NCBI E-utilities PubMed
- FDA prescribing information for SAXENDA (liraglutide), sections 1, 2, 5, 6.1 and 14.1, revision 2/2026
- FDA prescribing information for ZEPBOUND (tirzepatide), sections 1, 2, 3, 5, 6.1 and 14.1, revision 8/2026 DailyMed
- Pi-Sunyer X, Astrup A, Fujioka K, et al. A Randomized, Controlled Trial of 3.0 mg of Liraglutide in Weight Management. N Engl J Med. 2015 Jul 2;373(1):11-22. PMID 26132939, verified through NCBI E-utilities PubMed
- Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide Once Weekly for the Treatment of Obesity. N Engl J Med. 2022 Jul 21;387(3):205-216. PMID 35658024, verified through NCBI E-utilities PubMed