Weight Loss Injections Compared: Mounjaro vs Wegovy

The decision starts with mechanism, not just the numbers

Mounjaro activates two gut-hormone receptors: GIP and GLP-1. Wegovy activates one: GLP-1 only. In practice both medicines slow the speed at which food leaves your stomach, reduce hunger and affect how the brain registers fullness, but the dual-receptor action of tirzepatide appears to produce a somewhat different metabolic effect, which may partly explain the larger average weight reductions seen in head-to-head data.

In the SURMOUNT-5 trial (72 weeks, 751 adults with obesity and no diabetes), tirzepatide produced greater average weight loss than semaglutide 2.4mg, a finding that NICE's committee discussed when appraising tirzepatide in TA1026, published in December 2024. SURMOUNT-1 reported around 20–21% average body-weight reduction at the 15mg maintenance dose. The STEP 1 trial for semaglutide reported around 15% at the 2.4mg maintenance dose over 68 weeks. Both figures come from controlled trial conditions alongside lifestyle support, so treat them as context rather than a personal prediction.

There's also a newer dimension to the Wegovy picture. A dedicated single-dose 7.2mg Wegovy pen received MHRA approval on 14 April 2026, with trial data reporting around 20.7% average weight loss over 72 weeks, narrowing the gap with tirzepatide 15mg considerably. If you want to see how the two medicines stack up across a broader set of factors, our weight loss injection comparison page walks through the evidence in detail.

How the licensed eligibility criteria compare for each injection

The licensed criteria are similar for both, with some differences in the NICE-recommended thresholds for NHS access. At private prescription level, both medicines are licensed for adults with a BMI of 30 or above, or a BMI of 27 or above alongside at least one weight-related health condition such as high blood pressure, high cholesterol, type 2 diabetes or obstructive sleep apnoea. Lower BMI thresholds apply for certain ethnic backgrounds under UK clinical guidance.

On the NHS, NICE's recommendation for Wegovy (TA875) restricts it to specialist weight management services for a maximum of two years, with stricter comorbidity requirements. Tirzepatide's NICE appraisal (TA1026) sets a BMI threshold of 35 or above plus at least one qualifying condition for NHS access, with a phased rollout currently under way. If you're wondering about the NHS route in more detail, our page on how weight loss injections work in the UK covers the access picture clearly.

Private access through a regulated pharmacy like ours bypasses the NHS waiting list and the specialist-service requirement, subject to a prescriber confirming you're clinically suitable. A prescriber looks at the whole picture, not just your BMI number.

Side effects, tolerability and practical differences

Both injections share a broadly similar side-effect profile, because both slow gastric emptying. Nausea, loose stools, constipation, indigestion and fatigue are the most commonly reported effects, particularly in the first weeks after starting or after a dose increase. For most people these settle as the body adjusts, though not for everyone.

The MHRA's January 2026 Drug Safety Update on GLP-1 medicines flagged acute pancreatitis as an infrequent but serious risk: severe, persistent stomach pain that radiates to the back is a reason to get medical help promptly rather than waiting it out. You can report suspected side effects via the MHRA Yellow Card scheme, which also accepts reports of suspect sellers.

One practical difference worth knowing: women taking oral contraceptives who are prescribed Mounjaro should add a non-oral method of contraception for the first four weeks of treatment and for four weeks after each dose increase, because slowed gastric emptying can reduce pill absorption. NHS guidance does not identify the same concern for semaglutide. Discussing contraception plans is a standard part of a prescriber's assessment, our FAQs page has more on questions people commonly raise at that stage.

On the practical side, both come as pre-filled pens that you inject once a week and store in the fridge. Neither requires any needle changes or manual drawing up. Safe disposal of used pens matters, a sharps container is the correct way to do it.

Cost context and how to read the market

Since Eli Lilly raised Mounjaro's UK list price from around £122 to around £330 per four-week pen from 1 September 2025, private prices across the market typically range from roughly £149 to £375 per month depending on the dose and the provider. Wegovy pricing sits in a broadly similar range. These figures move, so treat them as a general steer.

What headline prices don't always make visible is what's included. Some providers quote a per-pen price that sits alongside consultation fees, prescription charges and delivery costs added separately. If you're weighing up your options, our guide to the best weight loss injections companies is a useful place to understand what separates a reliable service from one that cuts corners on care.

At nume, one price covers everything: the consultation, the prescriber's review, the medicine, and free next-working-day delivery. We're not the cheapest option available, that's a deliberate choice. For a prescription medicine dispensed through a GPhC-registered pharmacy, price is the wrong measure to lead with, and if you want to understand what makes a provider trustworthy, our page on the best company for weight loss injections sets out the standards worth looking for. If you're ordering around payday or before a bank holiday, the 12pm Monday-to-Friday cut-off for same-day dispatch is worth noting; check with our team if you're unsure about timing around a break.

The comparison below summarises the key factual differences between the two injections to help you come into a consultation with the right questions, and if you'd like to explore the options side by side before you do, our page where you can compare weight loss injections covers the main variables in one place.

Which of these injections suits you is a clinical decision our prescribers make with you, not a choice to settle by reading a table alone. If you're ready to start that conversation, check your eligibility with a free consultation.