The 60-second version
Ozempic and Mounjaro aren’t two versions of the same drug. Ozempic is semaglutide (a GLP-1 receptor agonist; the obesity brand is Wegovy). Mounjaro is tirzepatide (a dual GIP/GLP-1 agonist; the obesity brand is Zepbound). Two head-to-head trials now exist. For weight, the direct obesity trial (SURMOUNT-5) gave tirzepatide the edge: about 20% body-weight loss versus 14% for semaglutide at 72 weeks SURMOUNT-5 2025. For blood sugar, tirzepatide also lowered A1c more in a head-to-head diabetes trial SURPASS-2. But the strongest heart-protection evidence belongs to semaglutide, which cut major cardiac events about 20% in people with heart disease SELECT 2023 — tirzepatide hasn’t shown that. Both are prescription injectables with real gastrointestinal side effects and serious contraindications. “Which is better” is an individual medical decision, not a universal winner. This is education, not medical advice — talk to a doctor.
Educational journalism, not medical advice. Every claim here is checked against its cited sources by editor Tim Bunce — a health writer, not a physician. It isn’t specific to your situation: for health decisions, talk to your own clinician. How we work →
What each drug actually is
Both are weekly injectable peptides, but different classes. Semaglutide activates the GLP-1 receptor; it’s sold as Ozempic for type 2 diabetes and Wegovy for weight management (and Wegovy now also carries a cardiovascular-risk-reduction indication) FDA. Tirzepatide activates two receptors — GIP and GLP-1 — and is sold as Mounjaro for diabetes and Zepbound for weight management (and obstructive sleep apnea in obesity) FDA Wang 2024. The practical point: the brand names are marketing; there are really just two molecules, and they are not interchangeable.
Weight loss: the head-to-head
The only fair apples-to-apples comparison for weight is a direct trial. SURMOUNT-5 randomised 751 adults with obesity (without diabetes) to tirzepatide or semaglutide at their maximum tolerated doses for 72 weeks. Tirzepatide was superior: −20.2% body weight versus −13.7% for semaglutide (P<0.001), with greater waist reduction too SURMOUNT-5 2025. The single-drug obesity trials line up with that ranking — tirzepatide reached up to ~21% in SURMOUNT-1 SURMOUNT-1 and semaglutide ~15% in STEP-1 STEP-1 — but those were separate placebo trials in different people, so you can’t simply line up their numbers; SURMOUNT-5 is the valid comparison.
Blood sugar (type 2 diabetes)
There’s also a direct diabetes trial. SURPASS-2 compared tirzepatide against semaglutide (on top of metformin) in 1,879 adults with type 2 diabetes over 40 weeks. All tirzepatide doses produced greater A1c reduction (e.g. −2.30 vs −1.86 points; P<0.001) and more weight loss SURPASS-2. So on the two things these drugs are designed to do — lower weight and lower blood sugar — the head-to-head data favour tirzepatide on average SURMOUNT-5 2025 SURPASS-2.
Heart protection: semaglutide’s edge
Here the picture flips. The strongest cardiovascular-outcome evidence belongs to semaglutide: in SELECT (17,604 adults with overweight/obesity and established heart disease, no diabetes), semaglutide cut major adverse cardiovascular events by about 20% (hazard ratio 0.80) SELECT 2023. Tirzepatide’s cardiovascular-outcomes trial compared it against another GLP-1 drug (dulaglutide) and showed non-inferiority — it did not demonstrate superiority on hard cardiac endpoints, and it was never tested head-to-head against semaglutide for heart outcomes SURPASS-CVOT 2025. So if proven cardiac-event reduction is the priority, semaglutide currently has the better-established data SELECT 2023 SURPASS-CVOT 2025.
Side effects and safety
Both share the same dominant profile: gastrointestinal — nausea, vomiting, diarrhoea, constipation — mostly mild-to-moderate and concentrated during the dose build-up SURMOUNT-5 2025 SURPASS-2. In the head-to-head, GI side effects leading to stopping were a little more common with semaglutide than tirzepatide SURMOUNT-5 2025. Both also carry, at the label level, a boxed warning about thyroid C-cell tumours (and are contraindicated with a personal or family history of medullary thyroid cancer or MEN-2), plus risks including pancreatitis and gallbladder disease FDA. These are exactly the reasons they require a prescriber who screens for contraindications and monitors you.
The honest verdict
On the direct evidence, tirzepatide tends to deliver more weight loss and more A1c reduction SURMOUNT-5 2025 SURPASS-2, while semaglutide has the stronger proven heart-protection SELECT 2023. But “more weight loss on average” isn’t the same as “better for you.” The right choice depends on your other conditions, how you tolerate the side effects, what your insurance covers and what you can actually get, and your clinician’s judgment. There is no universal winner here — there’s a best fit for a specific person.
This article is educational journalism, not medical advice. Ozempic, Wegovy, Mounjaro and Zepbound are prescription medicines that require medical supervision, screening, and monitoring; never start, stop, switch, or source them based on an article. Do not buy or “compound” these from gray-market vendors. Talk to a qualified clinician about what’s right for you.
References
SURMOUNT-5 2025Aronne LJ, Horn DB, le Roux CW, et al. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity. N Engl J Med. 2025;393(1):26-36. (PMID 40353578) View source →SURPASS-2Frías JP, Davies MJ, Rosenstock J, et al. Tirzepatide versus Semaglutide Once Weekly in Patients with Type 2 Diabetes. N Engl J Med. 2021;385(6):503-515. (PMID 34170647) View source →SURMOUNT-1Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide Once Weekly for the Treatment of Obesity. N Engl J Med. 2022;387(3):205-216. (PMID 35658024) View source →STEP-1Wilding JPH, Batterham RL, Calanna S, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity. N Engl J Med. 2021;384(11):989-1002. (PMID 33567185) View source →SELECT 2023Lincoff AM, Brown-Frandsen K, Colhoun HM, et al. Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes. N Engl J Med. 2023;389(24):2221-2232. (PMID 37952131) View source →SURPASS-CVOT 2025Cardiovascular Outcomes with Tirzepatide versus Dulaglutide in Type 2 Diabetes (SURPASS-CVOT). N Engl J Med. 2025. (DOI 10.1056/NEJMoa2505928 — tirzepatide non-inferior to dulaglutide; superiority not met, HR 0.92.) View source →Wang 2024Wang L, et al. Insights into Natural and Engineered Peptide Analogues in the GLP-1, GIP, GHRH... Realms. Biomolecules. 2024;14(3):264. (PMID 38540684) View source →FDAU.S. FDA. Drug labels and approvals for Ozempic, Wegovy, Mounjaro and Zepbound (indications, boxed warnings, contraindications). View source →