Not Losing Weight on Semaglutide? Should You Switch to Tirzepatide? (October 2026)

01 · The verdict

Should you switch from semaglutide to tirzepatide?

Switching is worth discussing if you have taken semaglutide as prescribed, at the full licensed dose, alongside diet and activity changes, and your loss has stalled or never really started. Both medicines are effective, licensed treatments. In SURMOUNT-5, tirzepatide had the higher average loss, but that does not mean it will work better for you personally.¹⁵

Switching tends to suit you if: you have reached the 2.4mg Wegovy maintenance dose and held it for a sensible period, your prescriber agrees your response is below what you hoped for, and you have no reason (such as a past reaction) to avoid tirzepatide. Staying put tends to suit you if: you are still working up the dose ladder, you are losing steadily, or gastrointestinal side effects, not lack of effect, are your main problem. Side effects can occur on either medicine, so a switch is not an automatic escape from them.

Tirzepatide activates two gut-hormone receptors, GIP and GLP-1, while semaglutide acts on GLP-1 alone.¹ Semaglutide is a single-action GLP-1 medicine, so tirzepatide is a different option rather than just a higher dose of the same thing.

02 · Side by side

Tirzepatide vs semaglutide at a glance

These are trial averages from 751 adults; individual results vary.¹⁵ You can see current Mounjaro pen prices and consultation or compare the Wegovy pen directly.

03 · Deciding

The factors that should decide it

Three things matter more than the headline percentage. First, your history on semaglutide: dose reached, time on it and how you have tolerated it. Second, your health profile and any other medicines, which only a prescriber can weigh. Third, what you can sustain, because both medicines work alongside a reduced-calorie diet and more physical activity, not instead of them.²

04 · Check before switching

What to check before you switch

Start by confirming you have actually had a full trial of semaglutide. Wegovy steps up after at least four weeks through 0.25mg, 0.5mg, 1mg and 1.7mg, reaching the 2.4mg maintenance dose from week 17.¹⁸ If you are on a lower step, you may simply not have reached the licensed maintenance dose yet. Your prescriber can tell you whether that is the case.

Next, be realistic about what the trials show. 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 Those are averages, which means some people lose less than the average even when taking the medicine correctly. Falling short of 14.9% does not by itself mean you did anything wrong.

Then review the basics with your prescriber: whether doses were taken on schedule, how your eating and activity have changed, and whether any other medicines could be relevant. Treatment is designed to work alongside a reduced-calorie diet and increased physical activity.² Bringing a record of your weekly doses and weight to the consultation makes the conversation far more useful. Our free companion app, GLPTrackr, can help you keep that record.

Finally, ask whether the problem is lack of effect or something else. If side effects are the issue, say so plainly, because that changes the advice. In STEP 1, gastrointestinal side effects were reported by 74.2% of people on semaglutide 2.4mg compared with 47.9% on placebo, and 7.0% stopped treatment because of side effects.⁹

05 · How a switch works

How switching from semaglutide to Mounjaro works

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 your prescriber judges appropriate. That is often the 2.5mg starting dose, sometimes adjusted based on your history.¹¹

The pen comes in six strengths: 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg and 15mg.¹ Because you step up gradually, the first months of a switch can feel like starting again. That is normal and is part of how the dose is built up safely. If you step up after 4 weeks on each of 2.5mg, 5mg, 7.5mg and 10mg, your first four pens cost £959.96 at standard prices; a new customer's first order is £40 less, and every later order is £25 less.

Never run two GLP-1 medicines together. Do not take a leftover semaglutide dose alongside your first tirzepatide injection to ease the change over. Your prescriber will tell you exactly when to stop the old medicine and when to start the new one, and that timing is theirs to set.¹¹

If you have been taking Ozempic for weight loss, note that Ozempic 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. The licensed weight-management options are Mounjaro and Wegovy, and a regulated UK pharmacy will not supply Ozempic for weight loss.¹⁸

06 · What to expect on tirzepatide

What to expect after switching

Tirzepatide helps regulate appetite and slows how quickly the stomach empties. In practice, most people feel fuller sooner and less hungry between meals, which supports a reduced-calorie diet.¹ Do not expect it to override your eating habits; it makes them easier to change.

On results, the 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, compared with 3.1% with lifestyle changes alone. At 72 weeks, 85% of participants on 5mg, 89% on 10mg and 91% on 15mg had lost at least 5% of body weight. Half of participants on 10mg and 57% on 15mg lost at least 20%.² These are trial averages and individual results vary. As a worked example, for someone starting at 100 kg, 20.9% is about 21 kg. This is arithmetic on an average, not a prediction for you.

The most common side effects are nausea, diarrhoea, vomiting, constipation and abdominal discomfort, affecting more than 1 in 10 people; they are most likely when starting treatment or moving up a dose and for most people ease within days to a few weeks. Tell your prescriber about any new or worrying symptom, and you can report suspected side effects through the MHRA Yellow Card scheme.¹⁹ 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. Our team provides ongoing monthly reviews and side-effect support once you are a customer.

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 there is no way to speed it up.¹

07 · Shortcuts to avoid

Shortcuts and "poor man's Ozempic" options to avoid

A stalled result tempts people towards quick fixes. 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 combinations have no safety data and no regulated supply chain. If something promises faster results outside a licensed pathway, that is the warning sign.

"Natural GLP-1" supplements such as berberine, sometimes called the "poor man's Ozempic", are not medicines. They 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. They are not a substitute for a licensed treatment.

There is also no tablet form of Mounjaro; 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). They are different medicines with their own dosing, eligibility checks and trial results, so do not read their results against Mounjaro's. For current Wegovy tablet prices, see our weight loss treatments overview. Orlistat blocks some dietary fat absorption and produces smaller average losses, and Saxenda (liraglutide) is a daily injection, unlike once-weekly Mounjaro and Wegovy.

08 · Cost and NHS access

Cost, NHS access and how to start

A Mounjaro pen is one four-week supply. The Mounjaro pen costs £169.99 at 2.5mg, £218.99 at 5mg, £279.99 at 7.5mg and £290.99 at 10mg per month, rising to £329.99 at 15mg. Those are standard prices. New customers save £40 on their first order at any dose with code FIRST40, and an automatic £25 reorder discount applies to every future order (code DOSE25). Switching from another provider at 15mg? Your first order is £289.99. If you step up after 4 weeks on each dose, a first year 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, at standard prices before discounts.

Across the UK pharmacies we track, standard Mounjaro pen prices ranged from £143.96 to £339.00 as of 10 October 2026.

On the NHS, Mounjaro is available 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 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.

Ordering has three steps: complete the free online consultation, have it reviewed by a GPhC-registered prescriber (unsuitable orders are refunded automatically), then we dispense and dispatch. Same-day dispatch applies when ordered by 3pm, with free next-day tracked delivery in temperature-controlled packaging. Our Mounjaro comes through official LillyDirect supply, and all six doses are in stock. Ready to talk it through? Start your free consultation.

09 · Related guides

If it still isn't working

Plateaus can happen on any GLP-1 medicine. Our guide on what to do when semaglutide stops working covers the same decision from a different angle, and not losing weight with a GLP-1 looks at causes common to the whole class. If you have already moved over, see being on Mounjaro and not losing weight, or the dose-specific pages for 7.5mg, 10mg and 12.5mg.

Mounjaro (tirzepatide) is a prescription-only medicine, supplied only after an online consultation reviewed by a GPhC-registered prescriber. It is used alongside a reduced-calorie diet and increased physical activity. Individual results vary. This page is information, not a substitute for medical advice.

10 · 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