Until recently, Zepbound vs Wegovy was a question you could only answer by extrapolation, setting two separate trials side by side despite different populations, durations and protocols. SURMOUNT-5 changed that by giving both molecules to the same patients, in one trial, over the same period. The result at 72 weeks is clear: −20.2% of body weight with tirzepatide against −13.7% with semaglutide, a gap of 6.5 percentage points. One note first: Zepbound is the brand under which tirzepatide is approved for weight management in the United States, and Mounjaro is the same molecule sold elsewhere and for type 2 diabetes. This article covers what the trial showed, what 6.5 points means in pounds, and when Wegovy remains the better choice — because losing 13.7% of body weight is not a failure.
Zepbound vs Wegovy: what the head-to-head trial showed
In SURMOUNT-5, the only trial to give both molecules under identical conditions, tirzepatide produced 20.2% body weight loss at 72 weeks against 13.7% for semaglutide. The gap is 6.5 percentage points. This is the strongest evidence available on Zepbound vs Wegovy, and it rests on no extrapolation at all.
A head-to-head trial means a single protocol: the same inclusion criteria, the same duration, the same monitoring, and participants randomly assigned between the two arms. Earlier Zepbound vs Wegovy comparisons set separate trials against each other, whose participants shared neither starting weight, nor comorbidities, nor follow-up length. That produced an intuition, not a measurement. The results of SURMOUNT-5, published in the New England Journal of Medicine, change the nature of the answer.
One clarification worth making: the trial studied the molecules — tirzepatide and semaglutide 2.4 mg — not the boxes. Zepbound, Mounjaro and Wegovy are brand names, and which one applies depends on your country and your indication.
What 6.5 points actually means
Six and a half percentage points works out to roughly 11 to 15 lb (5 to 7 kg) depending on your starting weight. Here is the conversion, applying both SURMOUNT-5 rates to different starting weights. These are trial averages, not guaranteed individual results.
| Starting weight | Zepbound (−20.2%) | Wegovy (−13.7%) | Difference |
|---|---|---|---|
| 176 lb (80 kg) | about 35 lb (16 kg) | about 24 lb (11 kg) | about 11 lb (5 kg) |
| 198 lb (90 kg) | about 40 lb (18 kg) | about 27 lb (12 kg) | about 13 lb (6 kg) |
| 220 lb (100 kg) | about 45 lb (20 kg) | about 30 lb (14 kg) | about 14 lb (6.5 kg) |
| 243 lb (110 kg) | about 49 lb (22 kg) | about 33 lb (15 kg) | about 15 lb (7 kg) |
The other reading of that table matters at least as much. A 13.7% body weight loss sits well above the 10% threshold associated with improvement in obesity-related conditions. The Wegovy arm of SURMOUNT-5 did not fail: it produced a clinically meaningful result that happened to be smaller than the Zepbound arm. To place these numbers among the wider body of evidence, we have set out what the different doses cost and how coverage works separately, since cost often decides the question.
Zepbound and Wegovy: the full comparison
Beyond weight loss, Zepbound and Wegovy differ in mechanism, manufacturer, dose steps and approved indications. The table below gathers what separates the two treatments.
| Zepbound (Mounjaro elsewhere) | Wegovy | |
|---|---|---|
| Molecule | Tirzepatide | Semaglutide 2.4 mg |
| Receptors targeted | GLP-1 and GIP | GLP-1 only |
| Manufacturer | Eli Lilly | Novo Nordisk |
| Administration | Weekly injection | Weekly injection |
| Dose steps | 2.5 mg to 15 mg | 0.25 mg to 2.4 mg |
| Approved indications | See the European product record for tirzepatide | See the European product record for Wegovy |
| Weight loss in SURMOUNT-5 | −20.2% at 72 weeks | −13.7% at 72 weeks |
| Dominant adverse effects | Gastrointestinal | Gastrointestinal |
The mechanism difference deserves a sentence. Zepbound acts on two receptors, GLP-1 and GIP, whereas Wegovy activates only GLP-1. That is the pharmacological explanation most often offered for the gap measured in SURMOUNT-5.
Side effects: two similar profiles
Zepbound and Wegovy share the same dominant adverse-effect profile: gastrointestinal symptoms, mainly nausea, diarrhoea, constipation and vomiting. In both cases these concentrate in the weeks following each dose increase, during titration.
We are not publishing a table of adverse-event rates by trial arm here: those percentages do not appear in the sources we verified, and we do not quote figures without a source. The European product records linked above set out the safety profile of each treatment effect by effect. Since tolerability is highly individual, this is a point to discuss at an appointment rather than infer from a table.
Cost and coverage: the criterion that often decides
Between Zepbound and Wegovy, cost and insurance coverage frequently decide the question rather than the efficacy gap. Pricing and coverage vary enormously by country, by plan, and sometimes by indication within the same plan.
In the United States, coverage for weight-management indications differs markedly from coverage for type 2 diabetes, which is one reason the Zepbound and Mounjaro brands exist separately. Rather than fix figures that move, you can check your BMI and weight-loss projection to see where you sit before that conversation. A slightly less effective treatment that is affordable and sustained usually beats a more effective one stopped after three months on cost grounds.
When Wegovy is still the better choice
The SURMOUNT-5 gap does not make Wegovy obsolete. Several concrete situations justify preferring it to Zepbound, or staying on it rather than switching. All of them belong in a conversation with a clinician; none is a recommendation you can apply as written.
- You are already stable on Wegovy with a result you are satisfied with. Switching means restarting titration, with the gastrointestinal phase that comes with it, and no guarantee of a better individual outcome.
- You tolerate Wegovy well — something that cannot be predicted in advance and does not transfer from one molecule to another.
- Availability or coverage favours Wegovy where you live, a criterion that weighed heavily during the shortage periods.
- Your clinical situation involves evidence specific to semaglutide, depending on the indication your clinician is treating.
- You have a documented contraindication or intolerance to tirzepatide.
The position of this article fits in one sentence: presenting Wegovy as outdated would push stable patients to request a switch that has no clinical justification in their case.
Can you switch from Wegovy to Zepbound?
The switch exists and is done, but it is decided and organised with your prescriber. There is no dose equivalence between semaglutide and tirzepatide: a Wegovy dose does not convert into a Zepbound dose.
In practice, switching means restarting titration under the protocol specific to Zepbound, with the corresponding adjustment phase. We deliberately publish neither a conversion chart nor a schedule: those belong on a prescription, and a self-made transposition from an article risks both underdosing and overdosing. The question to bring to the appointment is simple: given my current result and my tolerability, is a switch indicated in my case?
Frequently asked questions
Is Zepbound more effective than Wegovy?
In the only head-to-head trial, yes: SURMOUNT-5 gives −20.2% for tirzepatide against −13.7% for semaglutide at 72 weeks, a 6.5 point gap. That gap is measured, not extrapolated. It does not mean Wegovy is ineffective, or that it is the wrong choice in every situation.
What is the difference between Zepbound and Wegovy?
Zepbound contains tirzepatide and acts on two receptors, GLP-1 and GIP. Wegovy contains semaglutide 2.4 mg and acts on GLP-1 only. Both are weekly injections, with different dose steps and approved indications that vary by country. Mounjaro is the same molecule as Zepbound under a different brand.
Can you switch from Wegovy to Zepbound?
Yes, but only with your prescriber, and with no dose equivalence between the two molecules. Switching means restarting a full titration under the Zepbound protocol. No conversion chart can be applied on your own from an article.
Which costs less, Zepbound or Wegovy?
It depends entirely on your country, your indication and your coverage. List price and actual out-of-pocket cost can diverge sharply, and coverage rules change. This criterion, more than the efficacy gap, often determines the choice made at the appointment.
Are the side effects the same?
The profiles are close: in both cases gastrointestinal effects dominate — nausea, diarrhoea, constipation, vomiting — and concentrate during dose escalation. Tolerability is highly individual: tolerating one well does not predict tolerating the other well.
Medical disclaimer. This article is strictly informational and does not replace medical advice. The figures cited are clinical trial averages and do not predict your individual result. Nothing here constitutes a treatment recommendation, a dose equivalence or a switching protocol: any decision to start, change or stop a treatment should be made with a healthcare professional. Information current as of 1 August 2026.
To track the effect on your own curve, logged data beats vague recollections on the day of your appointment: the MounjaGO app brings together weight, doses, side effects and meals, and turns them into a PDF report for your doctor — $12 for lifetime access, no subscription.