Tirzepatide vs Ozempic: what the trial data shows

What the head-to-head trial found, and why it matters for this comparison

The clearest direct evidence comes from SURMOUNT-5, a 72-week open-label trial published in the New England Journal of Medicine in 2025. It enrolled 751 adults living with obesity and no diabetes, and compared tirzepatide 15mg against semaglutide 2.4mg, the maintenance dose of Wegovy, the weight-loss-licensed form of semaglutide, not Ozempic. Tirzepatide produced a greater average reduction in body weight over the trial period. NICE's appraisal committee, reviewing SURMOUNT-5 alongside earlier data, noted that indirect comparisons also tended to favour tirzepatide.

That distinction about which semaglutide product was tested matters a great deal on this page. Ozempic tops out at 1mg weekly for diabetes management; Wegovy reaches 2.4mg (and now 7.2mg, following MHRA approval of a dedicated single-dose pen in April 2026). The semaglutide arm in SURMOUNT-5 used the 2.4mg weight-loss dose, so if you are wondering what is better, tirzepatide or Ozempic, comparing tirzepatide directly with Ozempic at its diabetes dose would produce an even wider gap in weight-related outcomes. Neither comparison tells you what will work best for you as an individual.

For a more granular look at how the two medicines rank when both are used for weight management, our page on whether tirzepatide outperforms Ozempic works through the evidence dose by dose.

Ozempic is licensed for diabetes, not weight loss

This is probably the single most important fact on this page, and it is worth sitting with for a moment. Ozempic (semaglutide, Novo Nordisk) is authorised by the MHRA for the management of type 2 diabetes in adults. The NHS medicines page for semaglutide is clear that Ozempic and Wegovy are different products for different purposes, even though they share an active ingredient. Prescribing Ozempic specifically for weight loss, outside a diabetes diagnosis, is off-label, a legitimate clinical tool in some circumstances, but not the same as a licensed weight-loss treatment with a dedicated evidence base and regulatory approval for that indication.

Tirzepatide, branded as Mounjaro in the UK, carries a full UK licence for weight management in adults with a BMI of 30 or above, or 27 and above where a weight-related condition such as high blood pressure or obstructive sleep apnoea is present. NICE recommended it in December 2024 (TA1026) for NHS use under specific criteria, and it is available privately through regulated services for people who meet the licensed criteria. If you are already on Ozempic and wondering whether a switch is sensible, the clinical and practical considerations are laid out on our Ozempic-to-tirzepatide switching page.

How the two medicines work, and where the mechanisms diverge

Both drugs slow how quickly food leaves the stomach and reduce appetite signals reaching the brain, but they do so through different receptor pathways. Semaglutide (Ozempic and Wegovy) is a GLP-1 receptor agonist, it mimics one gut hormone. Tirzepatide activates two receptors simultaneously: GLP-1 and GIP. It is the only dual-agonist weight-loss medicine licensed in the UK. Whether that dual action is what drives its stronger trial results is still being studied, but the clinical outcome data is consistent in showing tirzepatide's advantage.

Side effects for both medicines are largely gastrointestinal, nausea, loose stools, constipation, reflux and reduced appetite are the most commonly reported. These tend to be most noticeable in the first days after starting or after a dose step, then settle as the body adjusts. One practical habit worth building: check the batch number on your pen against the MHRA's Yellow Card reporting site before your first injection, it takes under a minute and is the simplest way to confirm your supply is genuine. The January 2026 MHRA Drug Safety Update also flagged acute pancreatitis as a recognised, though infrequent, risk with GLP-1 medicines; severe stomach pain reaching through to the back is a reason to seek medical help promptly rather than waiting.

Contraception deserves a specific note. Women using oral contraceptive pills who start tirzepatide are advised to add a non-oral method for the first four weeks of treatment and for four weeks after each dose increase, because slowed gastric emptying can reduce pill absorption. The same guidance does not currently apply to semaglutide. Details are set out by NHS England's weight-management injections guidance.

Comparing the two (a factual summary

If your interest is really in comparing tirzepatide with the weight-loss-licensed form of semaglutide rather than with Ozempic specifically, the tirzepatide vs Wegovy page covers that head-to-head in full, and our page on Wegovy vs Mounjaro approaches the same question from a different angle. Cost is a separate but related question, how the two compare on price is explained there without the noise of headline figures that often exclude consultation and aftercare.

What IS licensed and available for weight loss in the UK through a regulated private service is Mounjaro (tirzepatide) and Wegovy (semaglutide). Ozempic is not something nume prescribes for weight management. If you want to understand which of the two licensed options might suit your situation, or to find out whether you meet the clinical criteria, the right next step is a consultation with a prescriber who knows the full picture. Our treatment overview explains the process, and you can explore the weight loss options we offer before you decide anything. Which suits you is a clinical decision our prescribers make with you.