Wegovy vs Zepbound: What the Trials — and One Head-to-Head Study — Show

Wegovy and Zepbound are the two brand names people actually type into a search bar, more often than the molecule names behind them. Wegovy is semaglutide, approved by the FDA for chronic weight management in 2021. Zepbound is tirzepatide, approved for the same purpose in 2023. Here is what separates them beyond the name on the pen.

The pivotal trials, separately

Neither drug's headline weight-loss number comes from a trial that pitted the two brands against each other. Wegovy's comes from STEP 1: roughly 15% mean weight loss at 68 weeks, versus about 2.4% on placebo¹. Zepbound's comes from SURMOUNT-1: up to roughly 21% at the 15 mg dose over 72 weeks². Those numbers get cited constantly as if they were run under identical conditions — they weren't. Different trials, different populations, different follow-up windows. Treat a straight subtraction of the two headline percentages as suggestive, not proof.

The one real head-to-head that exists

A 2024 retrospective cohort study in *JAMA Internal Medicine* is the closest thing to a direct comparison available. Researchers matched over 18,000 adults with overweight or obesity who started either drug in routine clinical care and tracked on-treatment weight change³. Tirzepatide patients lost significantly more weight at every checkpoint: 2.4 percentage points more at 3 months, 4.3 more at 6 months, and 6.9 more at 12 months. They were also more likely to hit major thresholds — a hazard ratio of 3.24 for reaching 15% or more weight loss compared with semaglutide patients. Rates of gastrointestinal adverse events were similar between the two groups. This was a real-world EHR-based study, not a randomized trial, so it can't rule out that people prescribed one drug differed from people prescribed the other in ways researchers couldn't fully adjust for — but it is real evidence, not a marketing claim, and it points the same direction as the separate pivotal trials.

What each label carries that the other doesn't

Wegovy's FDA label expanded in March 2024 to include reducing the risk of cardiovascular death, heart attack and stroke in adults with established cardiovascular disease and obesity or overweight — the SELECT trial indication. That claim is unique to Wegovy; Zepbound's label does not carry it. Zepbound, in turn, is FDA-approved to treat moderate-to-severe obstructive sleep apnea in adults with obesity, based on the SURMOUNT-OSA trial — a claim Wegovy's label does not carry. If either condition applies to you, the drug-specific approval is worth knowing before the weight-loss percentage is. The full OSA evidence, including the actual trial numbers, is in Zepbound and sleep apnea; the cardiovascular story is in GLP-1, the heart and the kidneys.

Dosing and how long each stays active

Both are once-weekly subcutaneous injections with a slow titration schedule built to manage GI side effects — see GLP-1 dosage and titration schedules for the full week-by-week numbers. Semaglutide's elimination half-life is approximately one week, so Wegovy stays in circulation for roughly 5 to 7 weeks after the last dose; tirzepatide's half-life is approximately 5–6 days, so Zepbound clears in a comparable but slightly shorter window. Neither difference is large enough to be a deciding factor on its own — see how long GLP-1 drugs stay in your system if the timing matters for surgery, pregnancy planning, or switching.

How to actually decide

On the retrospective evidence, tirzepatide (Zepbound) tends to produce more weight loss for more people. That is a real point in its favor, not a reason to treat semaglutide (Wegovy) as the weaker choice by default — individual response varies, semaglutide has the longer real-world track record and the unique cardiovascular claim, and cost typically favors it on our board. If sleep apnea or established cardiovascular disease applies to you, the drug-specific label claim may matter more than either weight-loss number. For the mechanism-level comparison between the molecules themselves, including tolerability, read semaglutide vs tirzepatide; for the diabetes-labeled sibling of Zepbound, see Mounjaro vs Zepbound. Once you know which drug you want, CoreAge Rx carries both on one account, and the semaglutide and tirzepatide boards rank the field by molecule. The rest of the Desk's sourced evidence on these drugs is in the research library.