Weight Loss Injections Comparison Chart: Mounjaro vs Wegovy

Step 1: Know what each injection actually is

Start here, because a lot of confusion begins with a misunderstanding. Mounjaro and Wegovy are not the same medicine with different branding. Mounjaro contains tirzepatide, made by Eli Lilly, and works on two receptors: GIP and GLP-1. Wegovy contains semaglutide, made by Novo Nordisk, and targets GLP-1 alone. That single extra receptor pathway is the main reason the two medicines produce different results in trials, not that one is simply a newer version of the other.

One misconception worth laying to rest gently: Ozempic is also semaglutide, but it is licensed for type 2 diabetes, not weight management. It is not interchangeable with Wegovy for weight loss purposes, and the licensed weight loss injections in the UK are specifically Mounjaro and Wegovy. Rybelsus (oral semaglutide) follows the same rule, licensed for diabetes, not weight loss, where it is distinct from the Wegovy tablet approved in June 2026.

Both Mounjaro and Wegovy are delivered via pre-filled pens, once a week, into the abdomen, thigh or upper arm. Both slow gastric emptying and reduce appetite through gut-hormone pathways, which is why nausea and digestive side effects appear on both medicines' profiles. If you want to see how these two medicines stack up across every major factor before reading further, our weight loss injection comparison page sets them out side by side. The pharmacology underneath is meaningfully different; the injection routine is essentially the same.

Step 2: Compare the trial evidence and licensed doses side by side

The SURMOUNT-5 trial, published in the New England Journal of Medicine in 2025, randomised 751 adults with obesity but without diabetes to either tirzepatide or semaglutide 2.4 mg for 72 weeks. Tirzepatide produced greater average weight reduction. The gap narrows at Wegovy's newer 7.2 mg dose (approved by the MHRA on 14 April 2026) though direct comparative data at that dose is not yet available. A fuller breakdown of how results compare covers this evidence in more depth.

Trial figures are population averages. Individual results vary considerably, and no chart replaces the clinical assessment that weighs your health history, current medicines and circumstances.

Step 3: Look at eligibility and what each medicine costs in practice

The licensed eligibility criteria are similar for both injections: adults with a BMI of 30 or above, or 27 or above if at least one weight-related condition is present, such as high blood pressure, type 2 diabetes, high cholesterol, or obstructive sleep apnoea. Ethnic-background adjustments apply; UK guidance recommends thresholds 2.5 kg/m² lower for South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean backgrounds. You can read the full eligibility criteria including what a prescriber considers beyond BMI alone.

NICE's NHS thresholds are stricter than the licensed criteria, and the NHS rollout is phased, meaning most people accessing these medicines now do so privately. The cost of weight loss injections varies by provider, dose and what is included, consultation, prescription, aftercare and delivery are not always bundled into the headline figure. For context, the UK list price for Mounjaro rose significantly from September 2025, with reported private prices ranging roughly £149 to £375 per month depending on dose and provider.

Both are prescription-only medicines. Any legitimate supplier requires a clinical assessment before issuing one, as the criteria for a reputable provider make clear. The MHRA has warned publicly about counterfeit weight-loss pens sold without a prescription online, if a seller does not ask about your health history, that is a serious red flag.

Step 4: Understand the side-effect profiles before deciding anything

Both injections share a broadly similar side-effect profile because both slow gastric emptying. Nausea is the most commonly reported complaint, particularly after starting treatment or moving to a higher dose. Vomiting, diarrhoea, constipation, indigestion and fatigue also appear on both profiles, and most people find these settle within the first couple of weeks at a new dose. They are not trivial, but they are manageable for most people with sensible eating adjustments.

Pancreatitis is a known but infrequent risk with GLP-1 medicines. In January 2026, the MHRA issued a Drug Safety Update highlighting this: severe or persistent stomach pain that may spread to the back, with or without vomiting, warrants urgent medical attention. You should report any suspected side effects through the Yellow Card scheme, which covers both medicines.

Neither injection is recommended during pregnancy, breastfeeding or when actively trying to conceive. Women taking oral contraceptives alongside Mounjaro specifically are advised to add a non-oral method for the first four weeks of treatment and for four weeks after each dose increase, because tirzepatide's effect on gastric emptying may reduce pill absorption. NHS guidance notes no equivalent evidence of this interaction with semaglutide. Both medicines are for adults only; neither is licensed for under-18s.

Injection technique, site rotation and safe sharps disposal are practical matters worth covering before you start. A sharps container is needed for used pens. The NHS tirzepatide page and NHS semaglutide page both carry patient-level side-effect information in plain language.

If you are working through which injection suits your situation, check your eligibility with our prescribers, a real clinician reads every consultation the same day it arrives.