In clinical trials, Mounjaro (tirzepatide) at its maximum 15mg dose produced an average weight loss of 22.5% over 72 weeks (SURMOUNT-1). Wegovy (semaglutide) at its newer 7.2mg dose produced 20.7% over the same period (STEP UP). The gap between these two medications is now far narrower than most online guides suggest, and the right choice depends on your individual health profile, cardiovascular history, budget, and your clinician's recommendation.
How they work
Wegovy and Mounjaro both belong to a class of injectable medicines that mimic natural gut hormones to reduce appetite and help your body regulate blood sugar. The difference is in how many hormones each drug targets.
Wegovy is a GLP-1 receptor agonist. It mimics a single hormone, glucagon-like peptide-1 (GLP-1), which signals fullness to the brain and slows digestion. Mounjaro is a dual GLP-1 and GIP receptor agonist. It targets the same GLP-1 pathway as Wegovy, plus a second hormone called glucose-dependent insulinotropic polypeptide (GIP). GIP receptors are found in fat tissue and the brain, and activating them alongside GLP-1 appears to amplify the appetite-reducing and metabolic effects. This dual mechanism is the most likely reason Mounjaro typically produces greater average weight loss in clinical trials.
Weight loss results: what the trials show
Four datasets are relevant to this comparison in 2026.
SURMOUNT-1 (published New England Journal of Medicine, July 2022) studied 2,539 adults with obesity and without type 2 diabetes. Participants on tirzepatide 15mg lost an average of 22.5% of their body weight over 72 weeks, compared with 2.4% on placebo.
STEP 1 (published New England Journal of Medicine, February 2021) studied 1,961 adults with obesity and without type 2 diabetes. Participants on semaglutide 2.4mg lost an average of 14.9% over 68 weeks, compared with 2.4% on placebo.
STEP UP (published The Lancet Diabetes & Endocrinology, November 2025) studied 1,407 adults with obesity and without diabetes. Participants on semaglutide 7.2mg lost an average of 20.7% over 72 weeks, compared with 17.5% on the standard 2.4mg dose and 2.4% on placebo. The MHRA approved the 7.2mg dose in the UK in January 2026.
SURMOUNT-5 (published New England Journal of Medicine, July 2025; presented at the European Congress on Obesity 2025) was the first head-to-head comparison. It studied 751 adults with obesity and without diabetes. At 72 weeks, participants on tirzepatide achieved 20.2% weight loss compared with 13.7% on semaglutide. This trial compared tirzepatide at maximum tolerated dose (10mg or 15mg) against semaglutide at 2.4mg, not the newer 7.2mg dose.
| Metric | Mounjaro (15mg) | Wegovy (2.4mg) | Wegovy (7.2mg) |
|---|---|---|---|
| Average weight loss | 22.5% | 14.9% | 20.7% |
| Trial | SURMOUNT-1 | STEP 1 | STEP UP |
| Duration | 72 weeks | 68 weeks | 72 weeks |
| Cardiovascular outcome approval | Not approved | Approved (SELECT trial) | Approved (SELECT trial) |
The Wegovy 7.2mg dose has significantly closed the gap between these two medications. At maximum licensed doses, the difference in average weight loss is now approximately 2 percentage points (22.5% vs 20.7%), compared with the 8-percentage-point gap (22.5% vs 14.9%) that most existing comparison guides still reference. If you have read content suggesting Mounjaro produces dramatically more weight loss than Wegovy, check whether it accounts for the 7.2mg dose. Much of what is currently published does not.
These are results from separate trials with different populations. They cannot be directly compared as proof that one drug is more effective than the other for any individual patient. Your prescriber will consider your health profile, not headline trial figures, when recommending treatment.
Side effects: what's different
Both Mounjaro and Wegovy share a similar side-effect profile because they both activate the GLP-1 pathway. The most common side effects are gastrointestinal: nausea, vomiting, diarrhoea, and constipation. These typically occur during dose escalation and improve within the first few weeks at each new dose level. Most are mild to moderate in severity.
There are some measurable differences. In SURMOUNT-1, 6.2% of participants on tirzepatide 15mg discontinued treatment due to adverse events. In STEP UP, the equivalent figure for semaglutide 7.2mg was 5.4%. These figures come from separate trials and cannot be directly compared, but they give a general indication that tolerability is broadly similar. The Wegovy 7.2mg dose is associated with a higher incidence of dysaesthesia (altered skin sensations such as tingling or numbness), reported in approximately 23% of participants, compared with 6% on the 2.4mg dose. Most cases resolved while continuing treatment.
Wegovy has a stronger cardiovascular safety dataset. The SELECT trial (17,604 participants with pre-existing cardiovascular disease, mean follow-up 39.8 months) demonstrated a 20% reduction in major adverse cardiovascular events (MACE) with semaglutide compared with placebo. This led to Wegovy receiving a cardiovascular risk reduction indication. No equivalent cardiovascular outcomes trial has been completed for tirzepatide, although trials are underway.
In January 2026, the MHRA updated its product information for all GLP-1 and dual GLP-1/GIP medicines (including both semaglutide and tirzepatide) to highlight a small risk of severe acute pancreatitis, including rare reports of necrotising and fatal cases. Between 2007 and October 2025, the MHRA received 1,296 Yellow Card reports of pancreatitis across all GLP-1 medicines, of which 19 were fatal, in the context of 25.4 million packs dispensed. Anyone experiencing severe, persistent stomach pain should seek urgent medical attention. Suspected side effects can be reported via the Yellow Card scheme.
Cost in the UK (2026)
| Route | Mounjaro (tirzepatide) | Wegovy (semaglutide) |
|---|---|---|
| Foundry PAYG starter dose | £168/month (2.5mg) | £89/month (0.25mg) |
| Foundry PAYG maintenance dose range | £238–£308/month (7.5–15mg) | £128–£198/month (0.5–2.4mg) |
| Foundry Forge member starter dose | £139/month + £249/year (2.5mg) | £60/month + £249/year (0.25mg) |
| NHS route | GP prescribing via QOF (BMI 40+ with 4+ conditions; varies by practice) | Specialist weight management services only (NICE TA875) |
Prices are indicative for early 2026 and vary by provider. Always check whether the quoted price is all-inclusive. Consultation, needles, and delivery can add £30–£50 per month at some providers.
At Foundry, both Mounjaro and Wegovy are available with all-inclusive pricing: clinical assessment, prescribing, needles, and tracked cold-chain delivery included. Forge members cover all clinical and prescribing fees with a single annual payment of £249, making the total 12-month cost more predictable than pay-as-you-go ordering. The Forge membership applies across both medications, so switching mid-year does not incur additional fees.
Which one is right for you?
- Maximum weight loss is the primary goal.
- You do not have a history of cardiovascular disease.
- You are comfortable with a higher price for greater average efficacy.
- You want consistent access across all doses from 2.5mg to 15mg.
- You have existing cardiovascular disease or high cardiovascular risk.
- Cost is a deciding factor.
- You prefer a medication with a longer UK track record.
- Your clinician recommends it based on your health profile.
Both are available at Foundry with consistent stock across all doses. Your clinician will advise which is the better fit for your health profile and goals.
Frequently asked questions
Is Mounjaro better than Wegovy for weight loss?
In separate clinical trials, Mounjaro at its maximum dose (15mg) produced a higher average weight loss than Wegovy at its standard dose (2.4mg): 22.5% compared with 14.9%. With the newer Wegovy 7.2mg dose, the gap narrows to approximately 2 percentage points (22.5% vs 20.7%). Individual results vary significantly. Some patients respond better to one medication than the other based on their biology, tolerability, and adherence. Your prescriber is the best person to advise which is likely to work well for you.
Has the Wegovy 7.2mg dose changed the comparison?
Yes, materially. Before the 7.2mg dose, Mounjaro had a clear advantage in average weight loss across published trials. The STEP UP trial showed that semaglutide 7.2mg achieves 20.7% average weight loss over 72 weeks, bringing it much closer to tirzepatide's 22.5% in SURMOUNT-1. The SURMOUNT-5 head-to-head trial, which showed a larger gap (20.2% vs 13.7%), compared tirzepatide against the older 2.4mg semaglutide dose, not the 7.2mg. A head-to-head trial comparing tirzepatide to the 7.2mg dose has not been published. The MHRA approved the 7.2mg dose in the UK in January 2026, with a single-dose pen device approved in April 2026.
Is Wegovy cheaper than Mounjaro in the UK?
At equivalent treatment stages, yes. Wegovy is typically £50–£100 per month less expensive than Mounjaro at comparable dose levels through private providers. At Foundry, Wegovy starts at £89 per month PAYG (0.25mg starter dose), while Mounjaro starts at £168 per month PAYG (2.5mg starter dose). At maintenance doses, the difference is more pronounced: Wegovy 2.4mg is £198 per month PAYG at Foundry, compared with £238–£308 per month for Mounjaro at 7.5–15mg. All Foundry prices include clinical assessment, prescribing, needles, and tracked cold-chain delivery.
Can I switch from Wegovy to Mounjaro (or vice versa)?
Switching between GLP-1 medications is clinically possible and something prescribers manage regularly. Your prescriber will determine the appropriate starting dose on the new medication based on your current dose and how your body has responded. A dose re-escalation period is usually required, as the two drugs are not directly equivalent in dosing. If you are a Forge member at Foundry, your membership covers both medications, so switching does not incur additional clinical fees.
Which is available on the NHS: Mounjaro or Wegovy?
Both are available on the NHS, but access is limited and the routes differ. Mounjaro became available through GP prescribing from June 2025, but only for patients meeting strict Phase 1 criteria: BMI 40+ (37.5+ for some ethnic groups) with four or more qualifying conditions. From April 2026, prescribing sits within the GP QOF contract, and participation is optional at practice level, so availability varies by area. Wegovy is available through specialist weight management services under NICE TA875, not through GPs. For the majority of UK adults with a BMI of 30–39, the private prescription route remains the most realistic path to accessing either medication.
Can I get both Mounjaro and Wegovy at Foundry?
Yes. Foundry prescribes both Mounjaro and Wegovy across all licensed dose levels, with consistent stock. Your prescriber will recommend the medication best suited to your health profile during your clinical assessment. If you and your prescriber decide to switch medication at any point, Foundry supports that transition. The Forge annual membership covers clinical and prescribing fees for both medications, so your choice is guided by clinical suitability, not by what is available.
Not sure which is right for you? Foundry's clinical team prescribes both Mounjaro and Wegovy, with consistent stock across all doses. Your consultation includes a full clinical assessment, and your prescriber will recommend the treatment that best fits your health profile, goals, and budget. All-inclusive pricing, no hidden extras.
Check your eligibility in a few minutesTreatment is subject to prescriber approval and clinical suitability. Results vary between individuals. Wegovy 7.2mg pricing at Foundry is not yet confirmed and is excluded from the pricing table above. Shipping is charged separately at checkout.