Mounjaro and Wegovy: what's the difference between the two?

What the head-to-head trial actually showed

The most direct comparison between tirzepatide and semaglutide 2.4mg comes from SURMOUNT-5, a 72-week open-label trial published in the New England Journal of Medicine in 2025. Among 751 adults with obesity and without diabetes, tirzepatide produced a greater average body-weight reduction than semaglutide at the respective doses studied. That finding was reflected in NICE's appraisal of tirzepatide (TA1026), which noted that indirect comparisons across the programme favour tirzepatide, particularly at higher doses.

Looking at each medicine's own phase-3 data: SURMOUNT-1 (tirzepatide) reported an average weight reduction of around 20–21% at 15mg over 72 weeks. The STEP 1 trial for semaglutide 2.4mg (which ran 68 weeks) reported approximately 15% on average. It is worth noting that trial populations, durations and co-interventions differed, so these figures are not directly interchangeable. The newer Wegovy 7.2mg dose narrows the gap; the MHRA approved the dedicated 7.2mg single-dose pen on 14 April 2026, with trials reporting around 20.7% average loss over 72 weeks at that dose.

In short: tirzepatide has shown larger average reductions in most analyses to date, but semaglutide at 7.2mg has brought the two medicines considerably closer. Individual response varies, and trial averages are not personal predictions.

Mechanism, formulation and how each pen works

The core biological difference is the number of hormone receptors each medicine targets. If you want a fuller breakdown of how the two compare, our page covering what's the difference between Mounjaro and Wegovy goes through the mechanisms side by side. Tirzepatide (Mounjaro) is a dual GIP and GLP-1 receptor agonist, the only licensed weight-management medicine in the UK that activates both pathways simultaneously. Semaglutide (Wegovy) is a GLP-1 receptor agonist acting on a single pathway. Both slow gastric emptying and reduce appetite; the dual action of tirzepatide is the mechanism thought to account for much of the additional weight loss seen in trials.

Practically, both are once-weekly subcutaneous injections. Mounjaro is delivered via a KwikPen; Wegovy uses its own pre-filled pen format. Injection sites (abdomen, thigh or upper arm) are the same for both, rotated each week. Both require refrigerated storage; for exact room-temperature windows during transit or travel, the respective Patient Information Leaflets are the definitive reference. If needles are a concern, there is also now an oral option: the Wegovy tablet, approved by the MHRA on 11 June 2026, is a once-daily semaglutide pill. You can read more about the full range of options on our weight-loss treatment page.

Dosing ladders differ too. Mounjaro starts at 2.5mg and steps up in 2.5mg increments every four weeks as directed by your prescriber, through to 15mg. Wegovy begins at 0.25mg and titrates through several stages to its maintenance doses. A prescriber directs both schedules; titration is never self-managed.

Eligibility, where the licences and NICE criteria diverge

Both medicines share the same private-licence eligibility threshold: adults with a BMI of 30 or above, or 27 or above with at least one weight-related condition such as high blood pressure, type 2 diabetes or obstructive sleep apnoea. For some ethnic backgrounds, UK guidance applies thresholds 2.5 kg/m² lower. That is where the similarity largely ends on the NHS side.

NICE recommends tirzepatide (TA1026) for adults with a BMI of at least 35 and one or more weight-related comorbidities, through a phased NHS rollout. NICE's recommendation for semaglutide (TA875) adds an important restriction: it is approved for NHS use for a maximum of two years, within a specialist weight management service. The NHS rollout timetable, qualifying conditions and thresholds are explained on the weight management overview page. If you are considering the comparison through a private route, the process for accessing Wegovy privately follows a full prescriber-led assessment, as does Mounjaro, there is no shortcut for either.

One practical note: if you are trying to decide around a payday or a holiday, it is useful to know that both medicines require ongoing prescriber review before each repeat, so timing your first consultation to align with when you can commit to the early titration weeks is worth thinking through with our clinical team.

Side-effect profile: more alike than different

The side-effect landscape for Mounjaro and Wegovy is broadly similar, reflecting their shared mechanism of slowing gastric emptying. Nausea, loose stools, constipation, indigestion, burping and tiredness are the most commonly reported effects with both. Symptoms tend to be most noticeable after starting or following a dose increase, and often settle within a week or two. Injection-site reactions can occur with either.

There are some nuances. Tirzepatide's dual receptor activity means a slightly different hormonal profile, and some people tolerate one medicine better than the other, something that is difficult to predict in advance. Pancreatitis is a known but infrequent serious risk with GLP-1 medicines; in January 2026 the MHRA issued a Drug Safety Update flagging it. Severe, persistent stomach pain, particularly if it reaches the back, warrants urgent medical attention. Yellow Card reports for any suspected reaction can be made at yellowcard.mhra.gov.uk.

For women using oral contraceptives, tirzepatide specifically may reduce pill absorption during the first four weeks of treatment and for four weeks after each dose increase; adding a non-oral contraceptive method during those windows is the current clinical advice. A prescriber will cover this during your consultation. Our frequently asked questions address several of these practical points.

Which of these medicines suits your health profile is a clinical decision. Our prescribers at nume work through it with you, explore your options on the consultation page or read about Wegovy in more detail if semaglutide is where your interest lies. You can also find our guides on the difference between Manjaro and Wegovy and the Manjaro versus Wegovy comparison helpful if you have seen those alternative spellings in your research, alongside the Wegovy vs Ozempic comparison if semaglutide for diabetes has come up.