Ozempic vs Wegovy vs Mounjaro vs Zepbound.

You've been prescribed one of these four, or you're about to be, and the names all sound alike. They share a drug class, but the FDA labels are not interchangeable, the trial results are not identical, and your pharmacy will not swap one for another. Here is what is actually different.

One molecule, two brand names.

Ozempic and Wegovy contain the same active ingredient: semaglutide. Mounjaro and Zepbound contain the same active ingredient: tirzepatide. Inside each pair the molecule is identical. What differs is the dose strengths the FDA approved, the indication on the label, the packaging, and the price your insurance has agreed to.

Ozempic is labeled for type 2 diabetes. Wegovy is labeled for chronic weight management. Both are semaglutide, both are made by Novo Nordisk, and they are not substitutable at the pharmacy counter even though pharmacologically they are the same drug. Mounjaro is labeled for type 2 diabetes. Zepbound is labeled for chronic weight management and, since December 2024, for obstructive sleep apnea in adults with obesity. Both are tirzepatide, both are made by Eli Lilly.

Ozempic and Wegovy share an active ingredient. So do Mounjaro and Zepbound. The differences are in dose strengths, indications, packaging, and what your insurance is willing to cover.

How the two molecules actually work.

Semaglutide is a GLP-1 receptor agonist. It mimics the gut hormone GLP-1, which the body releases after a meal to signal fullness, slow gastric emptying, and prompt the pancreas to release insulin. Tirzepatide does the same thing at the GLP-1 receptor, and it also activates a second receptor for a related hormone called GIP. That makes tirzepatide a dual agonist. Semaglutide is a single agonist.

Whether the extra GIP activity is what drives the larger average weight loss seen in tirzepatide trials, or whether the effective dose is simply higher relative to semaglutide, is still being characterized in the literature. Both mechanisms are plausible; the clinical implications are still being worked out. The other oral member of this family, oral semaglutide (Rybelsus), uses the same molecule as Ozempic and Wegovy in a daily tablet form.

The key facts side by side.

The table below collapses the four products into one view. Numbers come from the current FDA prescribing information and the published phase 3 trials. Sources for every figure live in the Sources block at the end.

Two practical notes. The dose strengths matter because the starting dose is identical to its non-diabetes sibling (0.25 mg semaglutide, 2.5 mg tirzepatide), but the maximum dose differs between the diabetes and weight-management labels. And the pen design matters more than people expect: the multi-dose Ozempic pen requires a fresh needle each week, while Wegovy and the Zepbound autoinjector hide the needle entirely. If site rotation and needle handling are stressful for you, the pen form factor is worth raising with your prescriber.

What the weight-loss trials show.

The headline numbers come from three trials: STEP 1 for semaglutide, SURMOUNT-1 for tirzepatide, and SURMOUNT-5 for the only published head-to-head comparison.

In STEP 1, 1,961 adults with obesity (and without diabetes) on semaglutide 2.4 mg lost a mean of 14.9% of their body weight over 68 weeks, compared with 2.4% in the placebo arm. In SURMOUNT-1, adults with obesity on tirzepatide lost 16.0% (5 mg), 21.4% (10 mg), and 22.5% (15 mg) over 72 weeks, again against 2.4% on placebo.

SURMOUNT-5 is the trial most often cited in conversations about which to pick. It randomized 751 adults with obesity (no diabetes) to tirzepatide or semaglutide 2.4 mg, both titrated to maximum tolerated dose, for 72 weeks.

In the only published head-to-head trial of tirzepatide vs semaglutide for obesity, participants on tirzepatide lost an average of 20.2% of their body weight at 72 weeks. Participants on semaglutide 2.4 mg lost 13.7%.

That is a 47% relatively larger weight loss with tirzepatide in absolute terms (22.8 kg vs 15.0 kg). Roughly one in five tirzepatide participants hit 30% or more weight loss; roughly one in fifteen semaglutide participants did. Waist circumference fell 18.4 cm with tirzepatide and 13.0 cm with semaglutide.

For type 2 diabetes, the head-to-head is SURPASS-2. Semaglutide 1 mg lowered HbA1c by 1.86%; tirzepatide 5, 10, and 15 mg lowered it by 2.01%, 2.24%, and 2.30% respectively. All three tirzepatide doses outperformed semaglutide 1 mg statistically, though the absolute differences are small for many patients. The 2025 ADA Standards of Care list semaglutide and tirzepatide together as the highest-efficacy options for combined glycemic control and weight loss in T2D, without designating one as preferred.

Side effects: what the head-to-head actually showed.

Both molecules cause predominantly gastrointestinal effects: nausea, constipation, diarrhea, and vomiting, mostly during dose escalation and mostly improving over time. The interesting question is whether one is gentler than the other, and the answer depends on which dataset you read.

Pooled pharmacovigilance and placebo-controlled meta-analysis data show a higher relative risk of any GI event with tirzepatide vs placebo (RR ~2.94) than with semaglutide 2.4 mg vs placebo (RR ~1.68). On its face that suggests tirzepatide is harder on the gut.

But SURMOUNT-5, the only direct head-to-head, showed the opposite signal for treatment discontinuation: 2.7% of tirzepatide participants stopped because of GI adverse events vs 5.6% of semaglutide 2.4 mg participants. The two findings can coexist (different denominators, different placebo baselines, different real-world titration patterns), but the practical takeaway is that no clean ranking exists. GI tolerability is individual, and the best predictor of how someone will do on either drug is how their first few titration steps go.

One label change worth noting: in January 2026 the FDA asked manufacturers to remove the suicidal-ideation warning from GLP-1 labels after a 91-trial meta-analysis of 107,910 patients found no causal signal. The class-level warning is gone; the individual-level conversation with a prescriber is still warranted for anyone with a mental health history.

Heart and kidney outcomes.

This is the area where semaglutide currently has more completed data, and it is the area where the differences are most consequential for older readers and readers with comorbidities.

The SELECT trial (n = 17,604) found that Wegovy reduced major adverse cardiovascular events by 20% relative to placebo in adults with established cardiovascular disease and overweight or obesity, none of whom had diabetes. The curves separated within weeks; the effect was largely independent of how much weight participants lost. The FDA added a cardiovascular risk reduction indication to Wegovy's label in March 2024.

In January 2025 the FDA approved Ozempic for reducing the risk of worsening kidney disease, kidney failure, and cardiovascular death in adults with type 2 diabetes and chronic kidney disease, based on the FLOW trial. That made Ozempic the first GLP-1 with a kidney indication.

Tirzepatide does not yet have a completed cardiovascular outcome trial in obesity. SURMOUNT-MMO, the relevant trial (n > 15,000), is not expected to read out until October 2027. A post-hoc analysis of SURMOUNT-5 modeled 10-year predicted CV risk reduction as greater with tirzepatide than semaglutide, but that is a modeled prediction, not a hard endpoint.

Semaglutide has completed cardiovascular outcome data in two large trials. Tirzepatide's cardiovascular outcome trial, SURMOUNT-MMO, is not expected to read out until October 2027.

What people actually choose between in 2026.

In an ideal world the prescription would follow the clinical case. In practice, four external factors do most of the steering.

Insurance. Many commercial plans cover one of the four but not the others, based on formulary contracts negotiated with Novo Nordisk or Lilly. Substituting at the pharmacy counter does not work, even between Ozempic and Wegovy. Many people whose insurance covers one and not the other end up on whichever is covered.

The Medicare GLP-1 Bridge. Starting July 1, 2026, Medicare Part D will cover Wegovy and the Zepbound KwikPen at a $50 monthly copay for beneficiaries with BMI of 35 or higher, or 27 or higher with a weight-related comorbidity. This is a demonstration program and the eligibility rules are being finalized. It is the first time Medicare has covered GLP-1s for weight management at scale.

Shortage history. Both Wegovy and Mounjaro/Zepbound spent most of 2022 to 2024 on the FDA drug shortage list. The FDA removed tirzepatide on December 19, 2024 and semaglutide on February 21, 2025. With the shortages resolved, the 503A and 503B regulatory pathways that allowed compounding pharmacies to make compounded semaglutide and tirzepatide effectively closed by mid-2025. The $200 to $400 per month cash-pay route most people relied on during the shortage is no longer a legal supply path.

Pen design. Needle-phobic users tend to prefer Wegovy or the Zepbound single-use autoinjector, both of which hide the needle inside the device. People who prefer fewer total injection events sometimes prefer the multi-dose Ozempic pen (one cartridge covers roughly four weekly doses). Lilly launched a multi-dose KwikPen for Zepbound in 2024 and is rolling out a redesigned Mounjaro KwikPen in 2026, starting in the UK.

What to bring to the conversation.

This article is not a tool for picking a drug. It is a tool for showing up to the next clinic visit knowing what the choices mean. If you have questions about which of the four fits your situation, that conversation belongs with your prescriber. Questions that tend to be useful in that visit:

• Which of the four does my insurance currently cover, and what does the copay look like at the maintenance dose, not just the starting dose?
• If I am being prescribed one but my plan covers a different one, is the off-label substitution worth it for me, and who handles the prior authorization?
• How does the planned maintenance dose compare with the trial endpoint dose, and what does that mean for the result I should expect?
• If I have established cardiovascular disease or chronic kidney disease, does that change which molecule is preferred for me?
• What is the plan if I have to stop the medication, and how does my prescriber think about weight regain after stopping?

None of these has a single correct answer. The point of asking them is to make the trade-offs explicit before the prescription gets written.

This article is for educational purposes only and is not medical advice. It does not recommend any specific medication. Decisions about which GLP-1, if any, fits your situation belong with your prescriber. Read more about our editorial process and our terms.