Zepbound vs Wegovy: what the trials actually show

Zepbound and Wegovy are the two FDA-approved weight-management injectables that dominate the conversation — and the questions people ask about them. They are not the same drug, they are not made by the same company, and on the trial figures they do not produce the same amount of weight loss. But the honest comparison is more interesting than “one wins,” because each has a genuine advantage the other lacks.

What each one actually is

Zepbound is the obesity brand name for tirzepatide, made by Eli Lilly. It is a dual agonist: it activates both the GLP-1 receptor and the GIP receptor. (The same molecule is sold as Mounjaro for type 2 diabetes.)

Wegovy is the obesity brand name for semaglutide 2.4 mg, made by Novo Nordisk. It is a single GLP-1 receptor agonist. (The same molecule is sold as Ozempic for type 2 diabetes and as Rybelsus in an oral form.) The extra GIP pathway in tirzepatide is the mechanistic reason many expected it to drive more weight loss — and the head-to-head data bear that out.

The separate pivotal trials (not head-to-head)

Each drug earned its approval in its own placebo-controlled trial. In STEP 1, once-weekly semaglutide 2.4 mg produced a mean weight loss of −14.9% at 68 weeks versus −2.4% with placebo.^[2] In SURMOUNT-1, tirzepatide at its highest dose produced a mean reduction of −20.9% at 72 weeks versus −3.1% with placebo.^[1] Those numbers look decisive — but they come from different trials with different participants. Comparing them suggests an advantage for tirzepatide; it does not prove one.

The head-to-head trial: SURMOUNT-5

SURMOUNT-5 is the study that settled the obesity comparison on fair terms. It randomized 751 adults with obesity but without type 2 diabetes to the maximum tolerated dose of tirzepatide (10 or 15 mg) or the maximum tolerated dose of semaglutide (1.7 or 2.4 mg), once weekly for 72 weeks. At week 72, the least-squares mean weight change was −20.2% with tirzepatide versus −13.7% with semaglutide (P<0.001).^[3] Tirzepatide-treated participants were also more likely to reach weight reductions of at least 10%, 15%, 20%, and 25%, and lost more waist circumference. This is the strongest single piece of evidence on the question, because both drugs were used at their obesity doses in the same population.

Wegovy's distinguishing strength: cardiovascular outcomes

Weight loss is not the only thing that matters. In the SELECT trial, semaglutide 2.4 mg (Wegovy) was studied in 17,604 patients with established cardiovascular disease and overweight or obesity but without diabetes, and it significantly reduced major adverse cardiovascular events — cardiovascular death, nonfatal myocardial infarction, or nonfatal stroke — compared with placebo.^[4] That result underpins Wegovy’s additional FDA indication to reduce cardiovascular risk in adults with cardiovascular disease and obesity or overweight. Tirzepatide does not yet have an equivalent cardiovascular-outcomes approval. For a patient whose primary concern is heart risk, that distinction can outweigh a few extra points of average weight loss.

Side by side

Side effects and dosing

Both drugs share the same side-effect class. In SURMOUNT-5, the most common adverse events in both groups were gastrointestinal — nausea, diarrhea, constipation, vomiting — and most were mild to moderate and clustered during dose escalation.^[3] Both are started low and titrated up over months to limit those effects: Zepbound from a 2.5 mg starting dose toward a 5, 10, or 15 mg maintenance dose,^[5] and Wegovy through a stepped schedule toward 1.7 or 2.4 mg.^[6] Neither should be used with the other GLP-1 medicines, and both carry a boxed warning about thyroid C-cell tumors based on rodent data.^[5][6]

Cost and access

Neither list price is trivial, and coverage varies widely by plan, indication, and pharmacy. Because the two are made by different manufacturers, their savings programs, prior-authorization rules, and cash-pay options differ — which often matters more to the final decision than the trial numbers do.

The honest verdict

On average weight loss, the best available evidence — the SURMOUNT-5 head-to-head — favors Zepbound. But “more on average” is not “better for you.” Wegovy carries the dedicated cardiovascular-outcomes approval and a longer real-world track record, and the two share the same gastrointestinal side-effect profile. For someone optimizing purely for weight reduction, the data point to tirzepatide; for someone whose primary concern is cardiovascular risk, semaglutide’s outcomes data are a real edge. Tolerability, cost, and access decide most of the rest.

For the underlying molecule-level comparison, see our deeper read on tirzepatide vs semaglutide and on the semaglutide weight-loss trials. You can also line the two up feature by feature in our GLP-1 comparison tool.