Comparing Semaglutide and Tirzepatide for Weight Loss

What the head-to-head evidence shows

For years, comparing semaglutide and tirzepatide meant leaning on indirect analyses, different trials, different populations, different durations. SURMOUNT-5 changed that. The 2025 randomised trial, discussed in the NICE technology appraisal for tirzepatide (NICE TA1026), put the two medicines against each other directly in 751 adults with obesity and no type 2 diabetes over 72 weeks.

Tirzepatide produced greater average body-weight reduction than semaglutide 2.4mg. That is the most reliable comparison we have, two treatments, one trial, the same protocol. Across the broader SURMOUNT clinical programme, tirzepatide 15mg produced an average loss of around 20–21% of body weight; in some analyses of SURMOUNT-1 alone the figure reached approximately 22.5%. Semaglutide 2.4mg (Wegovy) produced around 15% average reduction in the 68-week STEP 1 trial.

The gap narrows at semaglutide's higher dose. The MHRA approved a 7.2mg semaglutide maintenance dose in 2026, and early results suggest average losses approaching tirzepatide 15mg territory, roughly 20.7% over 72 weeks. That dose is now available via dedicated single-dose pen. So while tirzepatide currently has the edge in the published head-to-head, the landscape is still shifting.

One clean comparison of the key figures is below.

Trial figures are population averages from clinical studies. Individual results vary. Sources: NEJM SURMOUNT-1; NEJM STEP 1; NICE TA1026; MHRA approval announcement, April 2026.

How the licences, eligibility and NHS access differ

Both medicines share the same private-prescription eligibility floor, adults with a BMI of 30 or above, or a BMI of 27 or above alongside at least one weight-related condition such as high blood pressure, raised cholesterol or obstructive sleep apnoea. Lower BMI thresholds apply for some ethnic backgrounds under UK clinical guidance. The prescriber weighs your full picture, not just the number on the scale.

NHS access is where they diverge more noticeably. Tirzepatide is being phased into primary care under NICE TA1026, with BMI and comorbidity thresholds that are progressively widening from 2025 through 2027, though GP participation is optional and waiting times vary. Semaglutide under NICE TA875 is restricted to specialist weight management services and carries a two-year treatment limit; NHS waiting lists for those services are commonly long.

For people who don't meet the current NHS thresholds, or who would rather not wait, private prescription through a regulated pharmacy is the practical alternative. If you're weighing up the two medicines specifically, our page on whether semaglutide or tirzepatide is right for you goes into the eligibility factors in more detail.

One thing that often surprises people: Ozempic is also semaglutide, but it is licensed for type 2 diabetes only, not weight management. Rybelsus is the same compound in tablet form, again for diabetes. The weight-loss semaglutide is Wegovy, and if you're wondering whether Mounjaro and Wegovy are actually the same medication, the distinction matters both legally and clinically.

Side-effect profiles and practical tolerability

The two medicines produce broadly similar side effects because both slow gastric emptying and reduce appetite through overlapping hormonal pathways. Nausea, loose stools, constipation, indigestion and fatigue are the most commonly reported, typically most noticeable in the first weeks or after a dose increase, then settling for most people.

The NHS medicines page for tirzepatide and the equivalent page for semaglutide set out the side-effect profiles in practical, patient-level detail and are worth reading before starting either. Pancreatitis is an infrequent but serious risk with GLP-1 medicines: the MHRA issued a Drug Safety Update in January 2026 highlighting it, and the message is clear, severe, persistent stomach pain that radiates to the back needs urgent medical attention.

For women using oral contraceptives, tirzepatide specifically can reduce pill absorption during the first four weeks of treatment and for four weeks after each dose increase, so an additional non-oral method is advised during those windows. NHS guidance does not flag the same concern for semaglutide. If you're also on HRT, it's worth discussing the form with your prescriber, transdermal options are generally preferred while taking tirzepatide for this reason.

Practically, both come as once-weekly injections you give yourself at home. Some people find the idea of injecting daunting; a question our prescribers hear regularly is whether the difference in mechanism means a meaningfully different injection experience. It doesn't, the pens work in a similar way, and most patients settle into a routine quickly. If you're curious about switching between the two, moving to tirzepatide after semaglutide is something that can be done with appropriate clinical oversight, and it's also worth knowing that our page on whether you can mix tirzepatide and semaglutide explains why taking both at the same time is not recommended.

Cost, what's included and which to choose

Tirzepatide is generally the more expensive of the two at the higher maintenance doses, a gap that widened after Eli Lilly revised UK list prices upward in September 2025, typical private prices since then range roughly £149–£375 per month depending on dose and provider, with the highest dose now commanding the steeper end of that range. Semaglutide pricing sits broadly within the same band at lower doses. If you'd like a fuller breakdown, our page comparing Mounjaro and Wegovy across cost, dosing and other key factors sets out the differences in detail, and a dedicated page also covers why Wegovy is priced differently to Mounjaro if you want the full breakdown.

At nume, one transparent price covers the consultation, the prescription, the treatment and aftercare, no subscription, no separate delivery charge, no hidden clinical fees. We don't aim to be the cheapest listing on a comparison site. For a prescription medicine, the right question isn't which costs least; it's which gives you safe, genuine, clinically supervised treatment. You can read more about how we work and verify our pharmacy on the GPhC register (registration number 9012878).

Which medicine suits you depends on your medical history, current medications, BMI, and what you've tried before. Our clinical team reviews every consultation personally, there's more about that approach on our clinical team page. Which suits you is a clinical decision our prescribers make with you, not one a comparison table can make for you.