Mounjaro vs Wegovy: What the Evidence Actually Shows

What the trial data says about weight loss with each medicine

Start with the numbers, because that is what most people actually want to know. SURMOUNT-1, involving 2,539 adults with obesity and no diabetes, reported average body-weight reductions of around 20–21% at tirzepatide 15mg over 72 weeks, with some analyses reaching approximately 22.5%. The STEP 1 trial, published in the New England Journal of Medicine, found semaglutide 2.4mg produced an average reduction of around 15% over 68 weeks in a similar population.

Then came SURMOUNT-5 — the first direct, head-to-head comparison. The trial ran for 72 weeks across 751 adults with obesity but without diabetes. Tirzepatide produced greater average weight loss than semaglutide 2.4mg. That is the most rigorous comparison available, and the full detail of what SURMOUNT-5 found is worth reading if results are a deciding factor for you.

It is also worth knowing that Wegovy is now available at a higher 7.2mg dose, following MHRA approval of a dedicated single-dose pen in April 2026. Early trial data at that dose reported approximately 20.7% average weight loss over 72 weeks, narrowing the gap with tirzepatide 15mg considerably. No head-to-head data exists yet for tirzepatide versus semaglutide 7.2mg. Clinical trials inform the decision; your prescriber makes it.

Where the differences really show up: mechanism, dosing and eligibility

The dual-receptor story matters clinically, not just as a headline. GIP and GLP-1 act together to slow gastric emptying, reduce appetite and support blood-sugar regulation. Activating both pathways appears to produce stronger appetite suppression for many people, which likely explains the larger average losses seen in the trials. If you want to understand the key differences between Ozempic and Mounjaro, the mechanism is again the clearest place to start, since both involve GLP-1 but work quite differently in practice. For those who have already tried how Wegovy compares from the other direction, the mechanism difference is the clearest explanation for the divergence in results.

Dosing starts at 2.5mg for Mounjaro, a lower starting point than Wegovy's 0.25mg, but the principle is the same: the opening weeks are about letting your system adjust, not about achieving maximum effect. Mounjaro titrates through 2.5, 5, 7.5, 10, 12.5 and 15mg; Wegovy through 0.25, 0.5, 1.0, 1.7 and 2.4mg (or now up to 7.2mg). A prescriber adjusts the pace based on how each individual tolerates the medicine, no table captures that judgment.

Eligibility on both NICE's tirzepatide recommendation (TA1026) and its semaglutide equivalent has ethnic-background adjustments: BMI thresholds can be 2.5 kg/m² lower for people of South Asian, Chinese, Middle Eastern, Black African or African-Caribbean backgrounds. BMI alone never settles the question, contraindications, existing conditions and current medicines all feed into what a prescriber can safely approve.

Side effects: largely similar, with one practical distinction

Both medicines share a GI-led side-effect profile: nausea, constipation, diarrhoea, indigestion, bloating and fatigue are the most commonly reported. These tend to be most noticeable in the first days after a new or increased dose, and they usually settle within a week or two for most people. The NHS tirzepatide page and the equivalent semaglutide page give the full lists in plain language.

One practical difference: women using oral contraceptive pills should add a non-oral method of contraception for the first four weeks of Mounjaro treatment and for four weeks after each dose increase. The concern is that tirzepatide slows gastric emptying enough to potentially affect pill absorption. NHS guidance does not flag the same requirement for semaglutide. It is a small procedural point, but it catches people off-guard. The practical differences between the two medicines page covers this and other day-to-day considerations in more depth.

The MHRA highlighted acute pancreatitis as an infrequent but potentially serious risk across GLP-1 medicines in a Drug Safety Update in January 2026. Severe, persistent stomach pain that radiates to the back is the symptom to take seriously immediately, and it applies to both medicines equally. Report any suspected side effects via the MHRA Yellow Card scheme.

NHS access, private routes and cost context

Access on the NHS follows different rules for each medicine. Tirzepatide became available through GP practices on the new contract from April 2026, with phased eligibility cohorts rolling out through 2026 and 2027, a fuller breakdown of how each medicine is accessed in the UK explains the NHS phases clearly. Wegovy remains available via specialist weight management services under NICE TA875, which requires multidisciplinary support for a maximum of two years, and waiting lists at those services are typically long.

Privately, both are available through GPhC-registered pharmacies following a clinical assessment. If you order by 12pm on a working day (even the Monday back from a bank holiday weekend, for instance), a prescriber at a registered pharmacy can review your case the same day. Cost is worth understanding clearly: Eli Lilly raised Mounjaro's UK list price from September 2025, and typical private prices since then range roughly £149–£375 per month depending on dose and provider, a detailed price comparison sets out what those figures actually include. For a Prescription-Only Medicine, the cheapest listing answers the wrong question; clinical oversight, a genuine supply chain and aftercare are the right metrics.

Our clinical team at nume reviews every consultation personally. Which medicine suits you (Mounjaro, Wegovy, or neither yet) is a clinical decision made with you, not for you.