Tirzepatide vs Semaglutide Weight Loss: The Difference in kg (October 2026)

01 · The verdict

Tirzepatide vs semaglutide: how many kg is the difference?

The difference is 7.8 kg on average in favour of tirzepatide, taken from SURMOUNT-5, where 751 adults took tirzepatide or semaglutide 2.4mg for 72 weeks. Average loss was 22.8 kg on tirzepatide and 15.0 kg on semaglutide.¹⁵ In percentage terms, adults on tirzepatide lost on average 20.2% of body weight versus 13.7% on semaglutide 2.4mg (Wegovy).¹⁵

That is a clear, trial-based difference in favour of tirzepatide, and SURMOUNT-5 is the first large head-to-head trial of the two. It does not make semaglutide ineffective. Both are licensed UK treatments, and which suits you depends on your health profile, how you tolerate each medicine and your prescriber's advice, not the headline number alone.¹⁵

If you want the broader picture, our guide to the full SURMOUNT-5 results goes further.

02 · Side by side

Tirzepatide and semaglutide compared

You can see current doses and prices on the Mounjaro pen page or compare with the Wegovy pen. All six Mounjaro doses are in stock.

03 · Deciding

What should decide it for you

Your priorities decide it, and the trial gap is only one factor. Tirzepatide had the larger average loss in the direct comparison. Semaglutide 2.4mg has its own substantial result, with adults in STEP 1 losing on average 14.9% of body weight over 68 weeks versus 2.4% on placebo.⁹ Do not compare that STEP 1 number with SURMOUNT results as if the trials were head to head. Only SURMOUNT-5 supports a direct comparison.

Practical factors worth discussing with a prescriber are your medical history, how you handled any previous GLP-1 medicine, and what you would aim to do over a year. Our head-to-head guide covers the trial design in more detail. When you are ready, a free consultation is reviewed by a GPhC-registered prescriber, with no charge and no obligation.

04 · Reading the kg gap

Why the kg gap depends on your starting weight

The 7.8 kg gap is an average, so your own difference will depend on where you start. The trial reported 22.8 kg versus 15.0 kg, which are the headline figures to use.¹⁵ Percentages scale with body weight, and kg figures do not scale the same way for everyone.

As a worked example, for someone starting at 100 kg, 20.2% is about 20 kg and 13.7% is about 14 kg.¹⁵ Someone starting lighter would see smaller kg numbers from the same percentages, and someone heavier would see larger ones. This is why percentage figures travel better between people than kg figures.

The same logic applies to SURMOUNT-1, where tirzepatide alongside diet and exercise gave average losses of 15% on 5mg, 19.5% on 10mg and 20.9% on 15mg over 72 weeks, versus 3.1% with lifestyle changes alone. For a 100 kg starting weight, 20.9% is about 21 kg.² These are trial averages, individual results vary, and treatment works alongside a reduced-calorie diet and more physical activity, not instead of them.²

Trial averages do not predict your own result, and the trials report outcomes at 68 and 72 weeks. For the percentage view, see our page on weight loss percentage by medicine.

05 · Beyond the average

How many people reach larger losses

The average hides how many people reach each milestone, and SURMOUNT-5 reports this clearly. At least 10% of body weight was lost by 81.6% on tirzepatide versus 60.5% on semaglutide. At least 15% was lost by 64.6% versus 40.1%, at least 20% by 48.4% versus 27.3%, and at least 25% by 31.6% versus 16.1%.¹⁵

The gap in the proportions grows at higher thresholds. Close to half of the tirzepatide group reached a 20% loss, against just over a quarter on semaglutide. Even so, many people on semaglutide reached meaningful losses, since 60.5% lost at least 10%.¹⁵

STEP 1 gives the semaglutide 2.4mg picture against placebo. Over 68 weeks, 86.4% lost at least 5% of body weight (placebo 31.5%), 69.1% lost at least 10% (placebo 12.0%) and 50.5% lost at least 15% (placebo 4.9%).⁹ Treat those as semaglutide-versus-placebo results, not as a comparison with tirzepatide.

For the trial that set tirzepatide against semaglutide on a different measure, our superiority guide explains how the trial tested the difference.

06 · Meta-analyses and other kg figures

Why you see different kg gaps online

Different kg gaps come from different studies, doses and durations, so they should not be blended into one number. Some summaries pool trials, include people with type 2 diabetes or compare lower doses. Others mix treatment periods, such as 68 weeks for one medicine and 72 for the other. Any of these will change the gap.

The SURMOUNT-5 result is 22.8 kg versus 15.0 kg over 72 weeks, a difference of 7.8 kg, in 751 adults on tirzepatide or semaglutide 2.4mg.¹⁵ It is a direct, same-trial comparison.

If you read a meta-analysis, check four things: which doses were compared, how long the treatment ran, whether participants had type 2 diabetes, and whether the result is a mean difference in kg or in percentage points. Our kg comparison page helps with reading these.

Brand names matter too. Ozempic is semaglutide licensed for type 2 diabetes, not a UK weight-loss medicine, and prescribing it privately for weight loss is off-label. The licensed weight-management options are Mounjaro (tirzepatide) and Wegovy (semaglutide 2.4mg), so for weight loss "Mounjaro vs Ozempic" is really Mounjaro vs Wegovy.

07 · How each one works

How tirzepatide differs mechanically

Tirzepatide activates two gut-hormone receptors, GIP and GLP-1, while semaglutide acts on GLP-1 alone. Together these help regulate appetite, slow how quickly the stomach empties and improve how the body responds to insulin. Most people feel fuller sooner and less hungry between meals, which supports a reduced-calorie diet.¹

Both are once-weekly injections. Tirzepatide has a half-life of about five days, so after a final dose it takes roughly 4–5 weeks to clear the system. Nothing needs doing while it clears, and it cannot be sped up.¹

Wegovy titrates 0.25mg, 0.5mg, 1mg, 1.7mg and then 2.4mg, stepping up after at least 4 weeks and reaching 2.4mg from week 17.¹⁸ Mounjaro comes in six strengths from 2.5mg to 15mg.¹

08 · Side effects and tolerability

Side effects: what to weigh alongside the kg

Weight lost is only half the picture, because gastrointestinal side effects are a real part of treatment. In STEP 1, gastrointestinal side effects were reported by 74.2% of people on semaglutide 2.4mg versus 47.9% on placebo, and 7.0% stopped treatment because of side effects versus 3.1% on placebo.⁹

The most common tirzepatide side effects, affecting more than 1 in 10 people, are nausea, diarrhoea, vomiting, constipation and abdominal discomfort. They are most likely when starting treatment or moving up a dose, and for most people they ease within days to a few weeks.[1,13] Your prescriber can talk you through them, and ongoing monthly reviews are part of our service.

Report any suspected side effect through the MHRA Yellow Card scheme.¹⁹ If you take insulin or sulfonylureas, doses may need adjusting because of the risk of low blood sugar, so tell your prescriber. Mounjaro slows stomach emptying, which can reduce how well oral contraceptive pills are absorbed. The SmPC advises switching to a non-oral method, or adding a barrier method (such as condoms), for 4 weeks after starting Mounjaro and for 4 weeks after each dose increase.¹ This applies to the pill only — implants, coils and injections are unaffected.

09 · Switching and cost

Switching between them, and what it costs

There is no licensed direct conversion between semaglutide and tirzepatide, so switching is done under prescriber supervision. Typically the previous medicine is stopped, a washout interval is observed, and Mounjaro is started at a dose the prescriber judges appropriate, often 2.5mg and sometimes adjusted based on your history. Never run two GLP-1 medicines together, and never combine Mounjaro with unlicensed "research" peptides or compounded copies.

On cost, the 2.5mg Mounjaro pen is £169.99 per month at the standard price, and the first four pens (2.5mg, 5mg, 7.5mg and 10mg) come to £959.96 before discounts. A new customer's first order is £40 less with code FIRST40, and every later order is £25 less (code DOSE25). A first year costs £2,711.88 if you settle at 5mg, up to £3,599.88 at 15mg, before discounts. Switching from another provider at a higher dose? The first-order discount applies at any dose.

Wegovy's first pen is £99.99 on a first order. Prices were checked 10 October 2026. Our Mounjaro comes from official LillyDirect supply, with free next-day tracked delivery and same-day dispatch when ordered by 3pm.

10 · Cheaper or natural alternatives

What about the "poor man's Ozempic"?

The phrase usually refers to supplements such as berberine, which are not medicines. They are not regulated for weight loss and have no comparable trial evidence. They are low-cost supplements with no clinical oversight, and dosing is not standardised. Treat any dramatic weight-loss claims for them with caution.

Licensed alternatives work differently. Orlistat (a tablet) blocks some dietary fat absorption and produces smaller average losses. Saxenda (liraglutide) is a daily injection, unlike once-weekly Mounjaro and Wegovy, and figures for it vary, so your prescriber can advise. Two GLP-1 weight-loss tablets are now licensed in the UK, Wegovy tablets and Foundayo, but they are different medicines with their own trial results. There is no tablet form of Mounjaro. Browse the full range of weight loss treatments for current options.

Mounjaro is a prescription-only medicine, supplied only after an online consultation reviewed by a GPhC-registered prescriber, and is used alongside a reduced-calorie diet and increased physical activity. Mounjaro is also available on the NHS, with access phased in over several years: NICE recommends it for adults with a BMI of at least 35 plus at least one weight-related condition, and the primary-care rollout began in June 2025 with the highest-need groups first.⁴ This page is information, not a substitute for medical advice.

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