Wegovy vs Zepbound: What the Head-to-Head Trial Shows and How to Choose

Wegovy and Zepbound are both once-weekly injections approved for weight management, and the core difference between them is one sentence long: Wegovy is semaglutide, which acts on a single gut-hormone receptor, and Zepbound is tirzepatide, which acts on two.

The short version. These are the two brands studied and labelled specifically for weight, at weight-specific doses, and they have now been compared directly in a single trial. Tirzepatide produced greater average weight reduction in that head-to-head; semaglutide holds the strongest published cardiovascular outcome evidence in people with obesity and no diabetes. Both work as ongoing treatment, not as a course you finish.

Wegovy vs Zepbound: The One Difference That Drives Everything Else

Both are once-weekly subcutaneous injections, and both were studied alongside reduced-calorie eating and increased physical activity. That is how they are meant to be used.

Wegovy is semaglutide, a GLP-1 receptor agonist: it mimics glucagon-like peptide-1, a hormone the gut releases after eating, which slows gastric emptying and signals fullness centrally. Zepbound is tirzepatide, which activates the GLP-1 receptor too, but also the receptor for glucose-dependent insulinotropic polypeptide, a second incretin hormone. Two receptors instead of one is the entire design premise.

Why that produces different results is not fully settled: in a randomized comparison in type 2 diabetes, tirzepatide reduced body weight and fat mass significantly more than semaglutide, yet appetite scores and measured energy intake did not differ (Heise et al., Diabetes Care, 2023, DOI).

Mounjaro and Ozempic are these same two molecules under their diabetes-labelled brand names; Wegovy and Zepbound are the weight-management versions at weight-management doses. Our overview of GLP-1 therapy in Ann Arbor covers the wider family.

The Head-to-Head Trial: What SURMOUNT-5 Found

Most comparisons of these two drugs set results from separate trials side by side. That is not a comparison. SURMOUNT-5 is.

751 adults with obesity and without type 2 diabetes were randomly assigned to the maximum tolerated dose of tirzepatide (10 mg or 15 mg) or of semaglutide (1.7 mg or 2.4 mg), once weekly for 72 weeks. The least-squares mean change in weight at week 72 was −20.2% (95% CI −21.4 to −19.1) with tirzepatide and −13.7% (95% CI −14.9 to −12.6) with semaglutide (P < 0.001).

Waist circumference fell 18.4 cm versus 13.0 cm, and tirzepatide participants were more likely to reach reductions of at least 10%, 15%, 20% and 25%. The most common adverse events in both groups were gastrointestinal, mostly mild to moderate and primarily during dose escalation (Aronne et al., N Engl J Med, 2025, DOI).

Two caveats belong in the same breath. The trial was open-label, and "maximum tolerated dose" means some semaglutide participants finished on 1.7 mg rather than 2.4 mg. Neither point erases a 6.5-percentage-point difference; both belong on the table.

Expected Results and Timelines

Semaglutide, STEP 1. 1,961 adults with a BMI of 30 or more, or 27 or more with a weight-related condition, and without diabetes, randomized 2:1 to 68 weeks of semaglutide 2.4 mg weekly or placebo. Mean weight change was −14.9% versus −2.4%, or −15.3 kg versus −2.6 kg, with at least 5% loss reached by 86.4%, 10% by 69.1% and 15% by 50.5% (Wilding et al., N Engl J Med, 2021, DOI).

Tirzepatide, SURMOUNT-1. 2,539 adults with the same broad entry criteria, randomized to 5 mg, 10 mg, 15 mg or placebo for 72 weeks. Mean weight change was −15.0%, −19.5% and −20.9% across the doses versus −3.1% with placebo, with at least 5% loss reached by 85% to 91% and 20% or more by 50% (10 mg) and 57% (15 mg) versus 3% on placebo (Jastreboff et al., N Engl J Med, 2022, DOI).

Those are averages; the spread inside them matters. Longer follow-up exists for tirzepatide — in the three-year SURMOUNT-1 analysis of participants with obesity and prediabetes, mean weight change at week 176 was −12.3%, −18.7% and −19.7% versus −1.3% with placebo, and 1.3% received a type 2 diabetes diagnosis versus 13.3% on placebo (hazard ratio 0.07), with no new safety signals identified (Jastreboff et al., N Engl J Med, 2024, DOI).

Dose Titration: Going Slowly Is the Strategy

Both drugs start low and step up, and that schedule is the main tool for keeping side effects manageable. In STEP 1, semaglutide was escalated over 16 weeks to the 2.4 mg weekly maintenance dose, and in STEP 4, 89.0% of participants reached it (Rubino et al., JAMA, 2021, DOI). In SURMOUNT-1, tirzepatide escalation spanned 20 weeks, with maintenance doses of 5 mg, 10 mg or 15 mg (Jastreboff et al., 2022, DOI).

Judging either drug at week eight is judging the titration, not the treatment. Titration should follow your tolerance, not a calendar.

Side Effects and How They Are Managed

Gastrointestinal effects dominate for both drugs, and both trials describe them the same way.

In STEP 1, nausea and diarrhea were most common with semaglutide, typically transient and mild to moderate, subsiding with time; 4.5% discontinued for gastrointestinal events versus 0.8% on placebo (Wilding et al., 2021, DOI). In SURMOUNT-1, gastrointestinal events were likewise most common with tirzepatide, mostly mild to moderate and primarily during escalation, with adverse-event discontinuation in 4.3%, 7.1% and 6.2% across the doses versus 2.6% on placebo (Jastreboff et al., 2022, DOI). SURMOUNT-5 reported the same pattern in both arms (Aronne et al., 2025, DOI).

A 2026 review in Nutrients is blunt about why this matters: gastrointestinal effects spanning nausea, vomiting, acid reflux, diarrhea and constipation are a major driver of discontinuation, targeted nutritional strategies may play a pivotal role in mitigating them, and most trials relied on generalized lifestyle advice, leaving practical guidance fragmented (Pardali et al., Nutrients, 2026, DOI).

Closing that gap is clinic work: hold a dose rather than escalate when symptoms are meaningful, adjust portion size and eating pace, manage fat and fiber, protect protein intake, and treat constipation early. Anything severe or persistent — severe abdominal pain, persistent vomiting, signs of dehydration — should be reported the same day.

What Happens If You Stop

This is the most important section on this page.

In the STEP 1 extension, 327 participants were followed for a year after treatment was withdrawn. Mean weight loss to week 68 had been 17.3%; by week 120 they had regained 11.6 percentage points of it, leaving a net 5.6% below baseline — roughly two-thirds of the loss regained — with cardiometabolic improvements reverting toward baseline. The authors concluded the findings confirm the chronicity of obesity and that ongoing treatment is required to maintain improvements (Wilding et al., Diabetes Obes Metab, 2022, DOI).

Tirzepatide behaves the same way. In SURMOUNT-4, participants lost a mean 20.9% during a 36-week lead-in, then were randomized to continue or switch to placebo. From week 36 to 88, weight changed by −5.5% with continued tirzepatide and +14.0% with placebo, and 89.5% of those continuing maintained at least 80% of their lead-in loss versus 16.6% of those withdrawn (Aronne et al., JAMA, 2024, DOI). STEP 4 found the mirror image for semaglutide: −7.9% with continued treatment versus +6.9% after switching to placebo (Rubino et al., 2021, DOI). Neither drug is a course you complete, and we would rather have that conversation at the beginning than at month 18.

Sleep Apnea and Cardiovascular Data: Where the Evidence Is Strong, and Where It Is Thinner

Here is what we know. The two are not in the same place on each question, and that asymmetry is genuinely useful when choosing.

Cardiovascular outcomes, semaglutide. SELECT enrolled 17,604 patients aged 45 or older with preexisting cardiovascular disease and a BMI of 27 or greater, without diabetes. A first major adverse cardiovascular event occurred in 6.5% on semaglutide 2.4 mg versus 8.0% on placebo (hazard ratio 0.80, 95% CI 0.72 to 0.90, P < 0.001) over a mean 39.8 months; 16.6% versus 8.2% discontinued for adverse events (Lincoff et al., N Engl J Med, 2023, DOI). This is the strongest cardiovascular outcome evidence either drug currently has in obesity without diabetes.

Cardiovascular outcomes, tirzepatide. SURPASS-CVOT randomized 13,299 patients with type 2 diabetes and atherosclerotic cardiovascular disease to tirzepatide or dulaglutide, an active comparator already shown to reduce cardiovascular events. The primary composite occurred in 12.2% versus 13.1% (hazard ratio 0.92, 95.3% CI 0.83 to 1.01), meeting noninferiority (P = 0.003) but not superiority (P = 0.09) (Nicholls et al., N Engl J Med, 2025, DOI). Different population, different comparator, different question — and we found no published placebo-controlled cardiovascular outcomes trial of tirzepatide in obesity without diabetes, so we will not imply one exists.

Sleep apnea, tirzepatide. SURMOUNT-OSA ran two 52-week randomized trials in adults with moderate-to-severe obstructive sleep apnea and obesity, one in people not using positive airway pressure and one in people using it. Mean baseline apnea-hypopnea index was 51.5 and 49.5 events per hour; change in AHI at week 52 was −25.3 versus −5.3 events per hour in the first trial and −29.3 versus −5.5 in the second, both P < 0.001, with improvements in hypoxic burden, high-sensitivity CRP and systolic blood pressure (Malhotra et al., N Engl J Med, 2024, DOI). We found no equivalent published trial for semaglutide at the weight-management dose, so we are not claiming one.

A network meta-analysis of 56 obesity pharmacotherapy trials in 60,307 patients maps the same split: semaglutide and tirzepatide were the two agents exceeding 10% total body weight loss; semaglutide reduced major adverse cardiovascular events and knee osteoarthritis pain; tirzepatide achieved remission of obstructive sleep apnea and metabolic dysfunction-associated steatohepatitis; both achieved type 2 diabetes remission and reduced heart failure hospitalization. Its closing recommendation is the one we take most seriously: individualize the choice (McGowan et al., Nat Med, 2025, DOI).

Cost and Access, Honestly

Coverage in the United States is inconsistent, varies by plan and employer, and changes. We verify benefits rather than guess. The published health economics is worth knowing but is not your pharmacy counter.

A US patient-level simulation built on the SURMOUNT-5 population estimated tirzepatide at maximum tolerated dose to be both less costly and more effective than semaglutide, with per-patient savings of $41,688 and 0.506 quality-adjusted life years gained (Johansson et al., J Med Econ, 2026, DOI) — though several authors are employed by the manufacturer of tirzepatide, which we flag rather than bury.

A shorter-horizon Greek payer analysis found the 72-week drug cost higher for tirzepatide (EUR 5,645.70 versus EUR 3,201.68), with semaglutide numerically cheaper per responder at lower weight-loss targets and tirzepatide favoured at higher ones, but overlapping confidence intervals at every threshold — no statistically significant difference in cost of control (Papantoniou and Maniadakis, Healthcare, 2025, DOI).

How the Choice Is Made at Arbour Longevity

We will not tell you which one you need from a web page. Here is what the decision turns on.

What else is going on. Moderate-to-severe sleep apnea puts the SURMOUNT-OSA data in the frame; established cardiovascular disease puts SELECT in the frame. These are the substance of the decision, not tiebreakers.

Your history with gastrointestinal symptoms. Reflux, gastroparesis, chronic constipation and poor tolerance of other medications all change how we titrate and sometimes what we start with.

Your target, your coverage, your continuity. The head-to-head difference widens at higher weight-loss thresholds, which is one of the few places the choice is genuinely evidence-driven. Beyond that, the best drug is the one you can stay on — and given the withdrawal data, that is not a minor consideration.

The plan around it. Weight is one number; we look at the rest, and treat medication as one component of medical weight loss rather than the whole plan. You can read more about semaglutide in Ann Arbor, tirzepatide in Ann Arbor and weight loss shots in Ann Arbor. Nothing on this page is a diagnosis or a recommendation for any individual.

Frequently Asked Questions

Is Zepbound just a stronger version of Wegovy?

No — they are different molecules. Semaglutide acts on the GLP-1 receptor; tirzepatide acts on GLP-1 and GIP. Tirzepatide produced greater average weight reduction head-to-head, −20.2% versus −13.7% at 72 weeks, but that is a difference between two drugs, not two strengths of one (Aronne et al., 2025, DOI).

How long before I see anything?

Both step up over months — 16 weeks of escalation in STEP 1, 20 in SURMOUNT-1 — and both trials ran to 68 and 72 weeks because weight was still falling (Wilding et al., 2021, DOI; Jastreboff et al., 2022, DOI).

Will I gain the weight back if I stop?

Much of it, for both drugs. A year after semaglutide withdrawal, participants had regained about two-thirds of their prior loss (Wilding et al., 2022, DOI). After tirzepatide withdrawal, weight rose 14.0% over 52 weeks while those continuing lost a further 5.5% (Aronne et al., 2024, DOI). We plan for that from the start.

Which one is easier on the stomach?

Neither trial programme shows one to be clearly gentler: gastrointestinal effects were most common for both, mostly mild to moderate and concentrated during escalation (Wilding et al., 2021, DOI; Jastreboff et al., 2022, DOI). Individual tolerance varies widely, which is why titration pace is personalised.

I have sleep apnea. Does that change the answer?

It is one of the clearest places the evidence differs. Two 52-week randomized trials in adults with moderate-to-severe obstructive sleep apnea and obesity found tirzepatide reduced the apnea-hypopnea index by 25.3 and 29.3 events per hour versus 5.3 and 5.5 with placebo (Malhotra et al., 2024, DOI). We found no equivalent published trial for semaglutide at the weight-management dose. Bring your sleep study.

I have heart disease. Does that change the answer?

It can, in the other direction. In 17,604 patients with preexisting cardiovascular disease and overweight or obesity but no diabetes, semaglutide 2.4 mg reduced the composite of cardiovascular death, nonfatal myocardial infarction and nonfatal stroke from 8.0% to 6.5% (Lincoff et al., 2023, DOI). Tirzepatide's cardiovascular trial ran in a different population against a different comparator and met noninferiority (Nicholls et al., 2025, DOI).

Can I switch from one to the other?

People do — for tolerance, coverage or plateau. Switching involves a fresh titration rather than a straight dose swap.

Wegovy and Zepbound Consultations in Ann Arbor

At Arbour Longevity we assess in person first, because the choice turns on your history, your other conditions and your coverage. Gandhi Bhattarai, FNP-BC, PMHNP-BC, Anti-Aging/Functional Medicine BC is a triple board certified nurse practitioner. We are at 2217 Packard St #15, in the Eastover Professional Center, Ann Arbor, MI 48104, open Thursday through Monday, 10am to 7pm, closed Tuesday and Wednesday. Parking is free and directly outside — no meters, no structure. Suite 15 is down a flight of stairs; if stairs are difficult for you, please call (734) 436-3357 before visiting so we can help. Call (734) 436-3357 or book your first visit. The first visit is $35, applied toward your treatment plan. Cash pay, HSA and FSA accepted.

Clinical information on this page is drawn from articles retrieved from PubMed and is provided for education. It is not medical advice, not a diagnosis, and not a promise of any individual result.