How Does Wegovy Work vs Mounjaro? (October 2026)

01 · The short answer

Wegovy vs Mounjaro: how they work and who each suits

The core difference is the number of receptors. Tirzepatide is the first treatment of its kind to activate both GIP and GLP-1 receptors at once, which together help regulate appetite, slow how quickly the stomach empties and improve how the body responds to insulin.¹ Semaglutide, the medicine in Wegovy, is a single-action GLP-1 medicine.¹

Both are effective, licensed treatments. In SURMOUNT-5, the first large trial that compares them head to head, tirzepatide produced the larger average loss.¹⁵ That does not make it right for everyone. Your health profile, how you tolerate treatment and your prescriber's advice matter more than a headline number.¹⁵

If you want the full side-by-side, our Wegovy and Mounjaro comparison goes further. For a results-only view, see whether Mounjaro or Wegovy works better.

02 · Side by side

Mounjaro and Wegovy compared

SURMOUNT-1 and STEP 1 were separate trials with different designs, so do not compare their figures against each other. Only SURMOUNT-5 supports a direct comparison. All figures are trial averages and individual results vary.

03 · Deciding

Which one suits you?

Both are effective, licensed treatments. Which suits you depends on your health profile, how you tolerate treatment and your prescriber's advice, not the headline number alone. Wegovy may suit you if your prescriber prefers semaglutide for your history, or if you have already taken it and tolerated it well.

Neither choice is permanent. Prescribers can review your response, and there is a supervised route between the two. Start with a free online consultation and a GPhC-registered prescriber will review which option is appropriate for you.

04 · How Mounjaro works

How Mounjaro works: two receptors at once

Mounjaro is the brand name for tirzepatide, a once-weekly injectable made by Eli Lilly. In the UK it is licensed for weight management in adults and for type 2 diabetes.¹

Tirzepatide activates the GIP and GLP-1 receptors together. These help regulate appetite, slow how quickly the stomach empties and improve the way the body responds to insulin.¹ In practice, most people feel fuller sooner and less hungry between meals, which supports a reduced-calorie diet.¹

Tirzepatide has a half-life of about five days. After a final dose it takes roughly 4–5 weeks to clear the system, and nothing needs doing while it clears.¹ It comes as a pre-filled multi-dose pen in six strengths: 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg and 15mg.¹ You can see current costs on the Mounjaro pen page, where all six doses are in stock.

05 · How Wegovy works

How Wegovy works: a single-action GLP-1 medicine

Wegovy is semaglutide at the 2.4mg maintenance dose, a once-weekly injection licensed for weight management. It is described as a single-action GLP-1 medicine, in contrast with tirzepatide's dual action.¹ The 2.4mg dose is the licensed maintenance dose.¹⁸

Dosing starts low and steps up. The pens are 0.25mg, 0.5mg, 1mg, 1.7mg and 2.4mg once weekly. The dose rises after at least 4 weeks, reaching 2.4mg from week 17.¹⁸

For more on what to expect from it, see our guides on how Wegovy works for weight loss and how quickly Wegovy works. You can check availability on the Wegovy pen page; a first pen starts from £99.99 as a first-order price.

06 · What the head-to-head shows

What SURMOUNT-5 shows

SURMOUNT-5 is the first large head-to-head trial of the two. Adults on tirzepatide lost on average 20.2% of body weight over 72 weeks versus 13.7% on semaglutide 2.4mg (Wegovy).¹⁵ Average loss was 22.8 kg versus 15.0 kg.¹⁵ For someone starting at 100 kg, 20.2% is about 20 kg and 13.7% is about 14 kg. Individual results vary.

The trial involved 751 adults for 72 weeks. The share of people reaching each threshold was higher on tirzepatide:¹⁵

Wegovy still works well for many people. In STEP 1, adults on semaglutide 2.4mg lost on average 14.9% of body weight over 68 weeks, compared with 2.4% on placebo. 86.4% lost at least 5%, 69.1% at least 10% and 50.5% at least 15%.⁹

Tirzepatide's own SURMOUNT-1 trial of 2,539 adults found average losses of 15% on 5mg, 19.5% on 10mg and 20.9% on 15mg over 72 weeks, against 3.1% with lifestyle changes alone.² These are trial averages, and treatment works alongside a reduced-calorie diet and more physical activity. For more on the maths, read whether Wegovy works better than Mounjaro.

07 · Downsides and side effects

What is the downside to Wegovy, and why do people stop?

The most common downside to Wegovy in trials was digestive side effects. In STEP 1, gastrointestinal side effects were reported by 74.2% of people on semaglutide 2.4mg, compared with 47.9% on placebo.⁹ 7.0% stopped treatment because of side effects, compared with 3.1% on placebo.⁹

With Mounjaro, mild nausea, altered appetite and tiredness in the first days after each injection are the commonest early effects and usually settle.¹ Our guide to Wegovy and Mounjaro side effects goes through each in detail.

For Mounjaro, the first days after each injection are when early effects are most likely, and they usually settle. If a symptom worries you, speak to your prescriber. You can also report side effects through the Yellow Card scheme.¹⁹

08 · Pace of results

How fast will you lose weight, and what about belly fat?

Weight loss on Mounjaro is gradual by design. The first weeks on 2.5mg are an adjustment phase and losses are usually modest. Most measurable progress builds from 5mg onward, month by month.

At three months, a sensible expectation on a standard titration is mid single digits as a percentage of body weight, with wide individual variation. The full 15–21% averages in SURMOUNT-1 were measured at 72 weeks, not 12.² So a large loss in three months is not what the trial averages suggest for most people. Think in months, not days. Our guide on how soon Wegovy works covers the early weeks.

Plateaus of a few weeks are normal as the body adapts to a lower weight. Review food intake honestly, protect protein and activity, check sleep and alcohol, and ask your prescriber whether a step-up is appropriate. A plateau is not a reason to double doses or add unlicensed products.

In trials, weight loss on tirzepatide came with average improvements in waist size, blood pressure, cholesterol and blood-sugar measures, and most participants with prediabetes returned to normal blood-sugar levels.² These are trial-average secondary outcomes, not promises.

Treatment response is reviewed by your prescriber. If you have lost less than 5% of your starting weight after 6 months on the highest dose you can tolerate, they will discuss whether to continue, adjust or stop.

09 · Switching between them

Switching from Wegovy to Mounjaro

There is no licensed direct conversion between semaglutide and tirzepatide. Switching is done under prescriber supervision. Typically the previous medicine is stopped, a washout interval is observed, and Mounjaro is started at a dose your prescriber judges appropriate. That is often the 2.5mg starting dose, sometimes adjusted based on your history.

Never run two GLP-1 medicines together. Mounjaro must also not be combined with unlicensed "research" peptides such as retatrutide, which has no UK licence, or with compounded copies. These combinations have no safety data and no regulated supply chain. Anything that promises faster results outside a licensed pathway is the warning sign.

If you switch to us, a new customer saves £40 on their first order at any dose with code FIRST40, and an automatic £25 reorder discount applies to every future order (code DOSE25). Standard prices are shown before those discounts.

Ozempic is semaglutide licensed for type 2 diabetes, so private prescribing for weight loss is off-label. The licensed weight-management options are Mounjaro and Wegovy, and a regulated UK pharmacy will not supply Ozempic for weight loss. If you are weighing older options, our Duromine comparison and Byetta comparison explain how they differ.

10 · Tablets and alternatives

Tablets, other options and the NHS

There is no tablet form of Mounjaro, because tirzepatide is injection-only in the UK. Two GLP-1 weight-loss tablets are now licensed: Wegovy tablets (oral semaglutide), approved by the MHRA in June 2026, and Foundayo (orforglipron), approved in August 2026.²⁰²¹ They are different medicines with their own dosing, eligibility checks and trial results, and both are prescription-only. For tablet pricing, see the weight loss treatments hub.

Orlistat (tablet) blocks some dietary fat absorption and produces smaller average losses. Saxenda (liraglutide) is another licensed injectable, but it is a daily injection, unlike once-weekly Mounjaro and Wegovy. "Natural GLP-1" supplements such as berberine are not medicines, are not regulated for this use and have no comparable trial evidence.

Mounjaro is available on the NHS, but access is being phased in over several years. NICE recommends it for adults with a BMI of at least 35 plus at least one weight-related condition. The NHS primary-care rollout began in June 2025 with the highest-need groups first, initially BMI 40+ with four or more qualifying conditions.⁴⁶ Full rollout is expected to take years, which is why many people who meet the licensed criteria choose regulated private treatment. NHS access to Wegovy runs through specialist weight-management services; ask your GP.

11 · Serious side effects

Serious side effects: when to get help straight away

Serious side effects are uncommon but need urgent attention. Seek immediate medical help for: severe, persistent stomach pain that may spread to your back, with or without vomiting (possible pancreatitis); pain in the upper right abdomen, fever or yellowing of skin/eyes (possible gallbladder problems); or signs of a severe allergic reaction such as swelling of the face or throat and difficulty breathing. If you take insulin or a sulfonylurea alongside Mounjaro, watch for low blood sugar (shakiness, sweating, confusion) — your prescriber may need to adjust those medicines.¹

12 · Cost and ordering

What each costs and how ordering works

The standard price of a 4-week Mounjaro pen runs from £169.99 at 2.5mg up to the 15mg pen at £299.99. Every later order is £25 off the standard price. If you step up after 4 weeks on each dose, your first four pens (2.5mg to 10mg) cost £879.96 at standard prices, before those discounts.

Across the UK pharmacies we track, standard Mounjaro pens ran from £143.96 to £319.99 per month across all doses (checked 24 October 2026).

Ordering has four steps:

• Complete a free online consultation, with no charge or obligation.
• A GPhC-registered prescriber reviews it. Payment is taken when you place the order; if the prescriber decides the treatment is not suitable, the order is refunded automatically in full.
• Our registered pharmacy dispenses it, with same-day dispatch when ordered by 3pm.
• Free next-day tracked delivery arrives in discreet, temperature-controlled packaging. Saturday delivery is £14.99.

Our Mounjaro is supplied through official LillyDirect supply, direct from Eli Lilly's UK distribution. Ongoing monthly reviews are included. Start on the Mounjaro pen page or read how Wegovy strengths line up with Mounjaro doses. You can also read how semaglutide compares with tirzepatide. Mounjaro is a prescription-only medicine, used alongside a reduced-calorie diet and increased physical activity. Individual results vary, and this page is information, not a substitute for medical advice.