Tirzepatide vs Semaglutide Weight Loss Effectiveness (October 2026)

01 · The verdict

Tirzepatide vs semaglutide: how does weight loss compare?

On average, tirzepatide lost more weight in the first large head-to-head trial. In SURMOUNT-5, adults on tirzepatide lost 20.2% of body weight over 72 weeks, versus 13.7% on semaglutide 2.4mg (Wegovy).¹⁵

Both are effective, licensed treatments. Which suits you depends on your health profile, tolerance and prescriber advice, not the headline number alone.¹⁵ A trial average does not predict your own result, and some people do better on semaglutide than the average suggests.

As a worked example, for someone starting at 100 kg, 20.2% is about 20 kg and 13.7% is about 14 kg. The trial itself reported average losses of 22.8 kg on tirzepatide and 15.0 kg on semaglutide.¹⁵ Starting weights differ, so the percentages are the fairer comparison.

A note on names. Mounjaro is the brand of tirzepatide. Wegovy is semaglutide 2.4mg. Ozempic is also semaglutide, but it is licensed for type 2 diabetes rather than weight loss, so a weight-loss comparison is really Mounjaro versus Wegovy.¹¹⁸

02 · Side by side

Tirzepatide and semaglutide at a glance

All six Mounjaro doses are in stock on the Mounjaro pen page, and the Wegovy pen is listed alongside it. Prices checked 11 October 2026.

03 · Decision factors

Who each option tends to suit

Tirzepatide had the larger average loss in SURMOUNT-5. The SURMOUNT-5 numbers favour it at every threshold from 10% to 25%.¹⁵

Semaglutide 2.4mg suits people whose prescriber prefers it given their history, or who have tolerated it well already.

Four factors usually decide the choice:

• Your health profile. Your prescriber weighs medical history, current medicines and weight-related conditions.
• Tolerance. Someone who has had trouble with one medicine may be advised differently.
• Prior experience. People already on Wegovy can be switched under supervision.
• Cost. Monthly price differs by product and dose. Our cost comparison sets this out in full.

If you want a prescriber to review which suits you, start your free consultation. Payment is taken when you place the order; if the prescriber decides the treatment is not suitable, the order is refunded automatically in full.

04 · How they work

How tirzepatide and semaglutide work differently

Tirzepatide is the first treatment of its kind to activate two natural gut-hormone receptors at once: GIP and GLP-1.¹ Together these help regulate appetite, slow how quickly the stomach empties, and improve the way the body responds to insulin. In practice, most people feel fuller sooner and less hungry between meals, which supports a reduced-calorie diet.

Semaglutide is a single-action GLP-1 medicine. That dual action is what distinguishes Mounjaro from semaglutide products such as Wegovy and Ozempic.¹

Both medicines are once-weekly injections, so the day-to-day routine is similar. Mounjaro is a pre-filled multi-dose pen, the KwikPen, in six strengths: 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg and 15mg. You usually start at 2.5mg and your prescriber steps up as you tolerate it. Our guide to Mounjaro's effectiveness covers how that titration unfolds.

Wegovy follows a fixed ladder. The pens are 0.25mg, 0.5mg, 1mg, 1.7mg and 2.4mg once weekly, stepping up after at least 4 weeks and reaching the 2.4mg maintenance dose from week 17. The 2.4mg dose is the licensed maintenance dose for weight management.¹⁸

Duration of action matters when you stop. Tirzepatide has a half-life of about five days, so after a final dose it takes roughly 4–5 weeks to clear the system. There is no way to speed this up, and nothing needs doing while it clears.¹

Neither medicine replaces lifestyle changes. A medicine that makes you feel full sooner makes eating less easier; it does not do the eating less for you.

In short, the mechanisms differ, the weekly routine is alike, and the dosing ladders differ. The evidence on which achieves more on average comes from trials.

05 · SURMOUNT-5 in detail

SURMOUNT-5: the head-to-head trial in detail

SURMOUNT-5 is the first large head-to-head trial of tirzepatide against semaglutide for weight loss. It enrolled 751 adults who took either tirzepatide or semaglutide 2.4mg for 72 weeks.¹⁵

The average results favoured tirzepatide: 20.2% of body weight lost versus 13.7% on semaglutide 2.4mg. In kilograms, the trial reported an average loss of 22.8 kg on tirzepatide against 15.0 kg on semaglutide.¹⁵ For someone starting at 100 kg, 20.2% is about 20 kg and 13.7% is about 14 kg. Your own result depends on your starting point and many other factors.

The threshold results show how the groups spread out:

• At least 10% lost: 81.6% on tirzepatide versus 60.5% on semaglutide.
• At least 15% lost: 64.6% versus 40.1%.
• At least 20% lost: 48.4% versus 27.3%.
• At least 25% lost: 31.6% versus 16.1%.

These figures matter because averages can hide how many people reach a given goal. The gap between the two groups holds at each threshold the trial reports.¹⁵ Plenty of people on semaglutide still lost at least 10% and many lost at least 15%.

What the trial does not tell you is how you will respond. A trial average is a description of a group, and the individuals within it vary widely. It cannot say whether you would lose more on one medicine, how you would tolerate either, or whether your own medical history makes one a better fit. That is the work of the prescriber consultation.

If you want to see how the percentages translate to different starting weights, our page on weight-loss superiority looks at that question in more depth.

The takeaway is simple and fair: on average, tirzepatide produced more weight loss than semaglutide 2.4mg over 72 weeks, and both are licensed, effective options.

06 · Each drug's own trials

What each medicine's own trials show

Each medicine also has a large pivotal trial of its own: SURMOUNT-1 for tirzepatide and STEP 1 for semaglutide 2.4mg. These were separate trials with different participants and durations, so their numbers must not be set side by side as if they were head-to-head. Only SURMOUNT-5 supports that comparison.

In SURMOUNT-1, 2,539 adults took tirzepatide alongside diet and exercise for 72 weeks. They lost on average 15% of body weight on 5mg, 19.5% on 10mg and 20.9% on 15mg, compared with 3.1% with lifestyle changes alone.² At 72 weeks, 85% of participants on 5mg, 89% on 10mg and 91% on 15mg had lost at least 5% of their body weight. Half of participants on 10mg and 57% on 15mg lost at least 20%.²

For someone starting at 100 kg, 20.9% is about 21 kg. As ever, these are trial averages and individual results vary. The treatment works alongside a reduced-calorie diet and increased physical activity, not instead of them.

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.⁹ Of those on semaglutide, 86.4% lost at least 5% of body weight (31.5% on placebo), 69.1% lost at least 10% (12.0%) and 50.5% lost at least 15% (4.9%).⁹ For someone starting at 100 kg, 14.9% is about 15 kg.

Why not simply compare 20.9% with 14.9%? Because the trials ran for different lengths (72 versus 68 weeks), enrolled different groups and used different comparators. The figures answer a different question: does each medicine work better than a control? Both do, clearly. The question of which works better for the same type of person under the same conditions is the one SURMOUNT-5 was built to answer.

Notice also that SURMOUNT-1 reports results by dose. Tirzepatide's average loss rose from 15% on 5mg to 20.9% on 15mg.

07 · Side effects and drawbacks

Side effects, tolerability and the drawbacks of each

Both medicines can cause gastrointestinal side effects, and tolerability is a real factor in the choice. In STEP 1, gastrointestinal side effects were reported by 74.2% of people on semaglutide 2.4mg, compared with 47.9% on placebo. Overall, 7.0% stopped treatment because of side effects, compared with 3.1% on placebo.⁹

The full list of side effects, and how often each occurs, is in the Mounjaro patient information leaflet.¹³ Reading it before you start is worthwhile whichever medicine you choose.

What are the drawbacks of tirzepatide? Honestly, they are practical as much as clinical:

• It is an injection given once a week; there is no tablet form of Mounjaro in the UK.
• It is prescription-only and needs a prescriber review before and during treatment.
• It works alongside a reduced-calorie diet and more physical activity, not instead of them.
• It has a cost, which varies by dose and provider.
• After a final dose it takes roughly 4–5 weeks to clear the system, and that cannot be sped up.
• Side effects are possible and are listed in the leaflet.

Do you lose more muscle on semaglutide or tirzepatide? Figures vary; your prescriber can advise.

Why do people say they feel so good on semaglutide? GLP-1 medicines help regulate appetite, so many people feel less hungry between meals. Whether that feels good is personal, and feeling unwell is a reason to speak to your prescriber, not to push on.

If you notice any new symptom, tell your prescriber. You can also report suspected side effects yourself through the MHRA Yellow Card scheme.¹⁹

Our ongoing monthly reviews and side-effect support exist for exactly these moments, and repeat orders re-check suitability rather than auto-shipping. For side-effect questions specific to one comparison, such as hair thinning, see our hair loss comparison.

08 · Licensing and alternatives

Licensing, diabetes, Ozempic and other options

Mounjaro and Wegovy are both licensed injectable options for weight management. Mounjaro (tirzepatide) is licensed in the UK for weight management in adults and for type 2 diabetes.¹ Wegovy is semaglutide 2.4mg, licensed for weight management.¹⁸

Ozempic is different. It is semaglutide licensed for type 2 diabetes. It is not a UK weight-loss medicine, and prescribing it privately for weight loss is off-label. A regulated UK pharmacy will not supply Ozempic for weight loss. So tirzepatide versus Ozempic for weight loss is really a comparison of Mounjaro with Wegovy. Our guide on whether Wegovy is semaglutide and how it compares with Mounjaro covers the naming in more detail.

If you have type 2 diabetes. Mounjaro improves blood sugar control (HbA1c) and supports weight loss in type 2 diabetes.⁸ Treatment and monitoring are coordinated differently in that case, so tell your prescriber and your usual diabetes team to keep care joined up.

Tablets. There is no tablet form of Mounjaro. Two GLP-1 weight-loss tablets are now licensed in the UK: Wegovy tablets (oral semaglutide, made by Novo Nordisk), approved by the MHRA in June 2026, and Foundayo (orforglipron, made by Eli Lilly), approved in August 2026.²⁰²¹ They are different medicines from Mounjaro, with their own dosing, eligibility checks and trial results, and both are prescription-only. Their results should not be set against tirzepatide's as if head-to-head; see the current Wegovy tablet listing on our site for prices.

Other licensed options. Orlistat is a tablet that blocks some dietary fat absorption and produces smaller average losses. Saxenda (liraglutide) is a daily injection, unlike the once-weekly Mounjaro and Wegovy. Figures for these vary, and your prescriber can advise.

The "poor man's Ozempic". This phrase is used for supplements such as berberine, also sold as "nature's Ozempic". They are not medicines, are not regulated for this use and have no comparable trial evidence. They are low-cost supplements with no clinical oversight, and dosing is not standardised. Marketing that makes dramatic weight-loss claims for them is a warning sign, not a reason to skip a proper assessment.

Unlicensed peptides. Be wary of anything promising faster results outside a licensed pathway. Mounjaro must not be combined with other GLP-1 medicines, unlicensed "research" peptides (such as retatrutide, which has no UK licence) or compounded copies. These have no safety data and no regulated supply chain. For a wider view of regulated choices, see all weight loss treatments.

09 · Cost and NHS access

Cost over a year, and NHS versus private access

Cost is a genuine part of the decision, so here is how it works for Mounjaro with us, all at standard prices before discounts. The 2.5mg starter pen is £169.99 for four weeks, and if you step up after 4 weeks on each dose, your first four pens (2.5mg to 10mg) cost £959.96. A new customer's first order is £40 less with code FIRST40, and every later order is £25 less (code DOSE25).

A first year (13 pens) costs £2,711.88 if you stay on 5mg after your 2.5mg starting pen, up to £3,599.88 if you step up through every dose to 15mg. Settle at a middle strength and your monthly price is £279.99 at 7.5mg, £290.99 at 10mg or £319.99 at 12.5mg. Per week, the strengths work out at £42.50 for 2.5mg, £54.75 for 5mg and £82.50 for 15mg.

Switching to us at a higher dose? The new-customer discount applies to a first order at any dose, so a first 15mg pen is £289.99 as a first-order price.

For context, across the UK pharmacies we track, Mounjaro pens range from £143.96 to £339.00 per month depending on dose and provider, as checked on 11 October 2026. The gap between providers for the same dose ranges from £27 to £41. For Wegovy, see the Wegovy pen page for current prices.

NHS or private? 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, and 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 rather than waiting.

NHS access to Wegovy runs through specialist weight-management services; ask your GP.

The NHS prescription charge in England is £9.90 where it applies. Private treatment is paid for in full, and our consultation is free: the price shown is the price paid, with no hidden fees. Payment options include Visa, Mastercard, Klarna and pay-monthly plans, with no subscriptions.

10 · Switching and what not to mix

Switching between them, and what not to mix

There is no licensed direct conversion between semaglutide and tirzepatide, so switching is always 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. Your prescriber sets the interval and the dose.

Why would someone switch from semaglutide to tirzepatide? Usual reasons are that results have plateaued or fallen short of what the person hoped for. Others switch because of tolerance or because their prescriber advises it. Either way, the decision belongs to the prescriber, not to a calculator.

Why would a doctor prescribe semaglutide instead of tirzepatide? Reasons include your health profile, how you tolerated treatment before, and clinical judgement. Wegovy follows a defined four-week step-up ladder to a single maintenance dose.¹⁸ A higher average in a trial does not make tirzepatide right for every individual.

What not to mix with semaglutide, or tirzepatide? The clear rule is never to run two GLP-1 medicines together. Do not take Wegovy and Mounjaro at the same time, and do not add Ozempic, other GLP-1 medicines, unlicensed "research" peptides, compounded copies or so-called stacks. There is no safety data for these combinations and no regulated supply chain. If something promises faster results outside a licensed pathway, that is the warning sign.

For other medicines you take, including ones for diabetes, tell your prescriber and read the patient information leaflet.¹³ Never change doses of other medicines on your own.

Does semaglutide ever work better than tirzepatide? For individuals, yes it can. The trial results are averages, and a trial average does not predict your own result. Some people lose more on semaglutide than the tirzepatide average, and some tolerate it better. That is why the choice is made with a prescriber.

How ordering works with us

If you decide on Mounjaro, the process has four stages. First, complete a free online consultation, a short health questionnaire with no charge and no obligation. Second, a GPhC-registered prescriber reviews your consultation; payment is taken when you place the order, and if the prescriber decides the treatment is not suitable, the order is refunded automatically in full. Third, our registered pharmacy dispenses, with same-day dispatch when ordered by 3pm. Fourth, free next-day tracked delivery arrives in discreet, temperature-controlled packaging; Saturday delivery is £14.99.

Mounjaro is supplied through official LillyDirect supply, so you receive genuine KwikPens direct from Eli Lilly's UK distribution. Needles, a sharps bin and injection guidance come with every order. Ongoing monthly reviews and the free GLPTrackr app support you afterwards. Ready to begin? Start your free consultation.

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