Long Term Effects of Tirzepatide vs Semaglutide (October 2026)

01 · The verdict

Which suits long-term use: tirzepatide or semaglutide?

Neither is simply "better for long-term use" in a way the evidence can prove. Tirzepatide produced bigger average weight loss in the first large head-to-head trial, SURMOUNT-5.¹⁵ Both are effective, licensed treatments, and the right one depends on your health profile, tolerance and prescriber advice, not the headline number alone.¹⁵

Tirzepatide may suit you if your priority is the largest average weight loss seen in a direct comparison and you have no history that makes your prescriber cautious. Semaglutide 2.4mg may suit you if you already tolerate it well, or your prescriber prefers a single-action GLP-1 medicine for your circumstances. If you are weighing the two on price, our full tirzepatide and semaglutide comparison covers more of the day-to-day differences.

The honest limit of any comparison is time. The trials behind these figures ran 68 to 72 weeks. Ongoing review with a prescriber is how long-term safety is managed in practice.

02 · Side by side

Tirzepatide vs semaglutide: trial results and key differences

The table uses trial averages with the trial named. Only SURMOUNT-5 supports a direct comparison between the two; the other rows come from separate trials and should not be read against each other.

You can see current dose prices on the Mounjaro pen page and the Wegovy pen page. All six Mounjaro doses are in stock, and prices were checked 10 October 2026.

03 · Deciding

Factors that matter more than the headline number

Five practical factors decide most real-world choices. First, your medical history: pancreatitis, gallbladder problems, severe gut disease and diabetic retinopathy all make a prescriber more careful.¹ Second, how you tolerate gut side effects. Third, whether you are already on one medicine and doing well. Fourth, cost over a year. Fifth, whether you will keep up the diet, protein and activity habits that both licences assume.

If you are moving from semaglutide, there is no licensed direct dose conversion. Switching is done under prescriber supervision, usually with the earlier medicine stopped and a washout interval observed. The new medicine then starts at a dose your prescriber judges appropriate.¹ Our free consultation is reviewed by a GPhC-registered prescriber, who can take your history into account and recommend which medicine fits.

04 · What long-term evidence exists

What long-term evidence actually exists

SURMOUNT-1 followed 2,539 adults on tirzepatide for 72 weeks.² STEP 1 followed adults on semaglutide 2.4mg for 68 weeks.⁹ SURMOUNT-5 compared the two directly in 751 adults over 72 weeks.¹⁵

That matters because "long-term effects" can mean three different things. One is how much weight is lost and kept while on treatment. Another is side effects that appear or fade with time. The third is rare harms that only show up after very large numbers of people have taken a drug for years. The third is where honesty requires saying that no trial can fully answer it yet.

It also helps to separate the two ways these medicines are licensed. Mounjaro is licensed in the UK for weight management and for type 2 diabetes.¹ Wegovy is semaglutide 2.4mg licensed for weight management, while Ozempic is semaglutide licensed for type 2 diabetes and is not a UK weight-loss medicine.¹⁸ Comparing results across those indications can mislead, because diabetes trials and obesity trials enrol different people and measure different outcomes.

Where do we expect new information to come from? Longer follow-up of the existing trials, continued safety monitoring, and reports through the MHRA Yellow Card scheme.¹⁹ If you have a symptom you think may be linked to either medicine, report it. Our guide on what we know about long-term GLP-1 effects goes further into this evidence gap.

The practical reading is simple. Over 68 to 72 weeks, both medicines produced substantial average weight loss alongside a reduced-calorie diet and increased activity. Beyond that window, you are relying on ongoing clinical review, not on a trial that has already answered every question.

05 · Weight loss over 72 weeks

Weight loss over 72 weeks: the head-to-head numbers

In SURMOUNT-5, adults on tirzepatide lost on average 20.2% of body weight over 72 weeks, versus 13.7% on semaglutide 2.4mg.¹⁵ In kilograms, the average loss was 22.8 kg on tirzepatide and 15.0 kg on semaglutide.¹⁵ As a worked example, for someone starting at 100 kg, 20.2% is about 20 kg and 13.7% is about 14 kg. These are trial averages, and individual results vary.

The spread of results is as informative as the average. At least 10% of body weight was lost by 81.6% of people on tirzepatide and 60.5% on semaglutide. At least 15% was lost by 64.6% versus 40.1%. At least 20% was lost by 48.4% versus 27.3%. At least 25% was lost by 31.6% versus 16.1%.¹⁵ More people on tirzepatide reached each threshold, but plenty on semaglutide did too.

The separate trials fit the same picture, but should not be set side by side as a head-to-head. In SURMOUNT-1, people on tirzepatide plus diet and exercise lost on average 15% of body weight on 5mg, 19.5% on 10mg and 20.9% on 15mg over 72 weeks, compared with 3.1% with lifestyle changes alone.² In STEP 1, adults on semaglutide 2.4mg lost on average 14.9% over 68 weeks, versus 2.4% on placebo.⁹

STEP 1 also reported that 86.4% of adults on semaglutide 2.4mg lost at least 5% of body weight, compared with 31.5% on placebo. In that trial, 69.1% lost at least 10% (versus 12.0%) and 50.5% lost at least 15% (versus 4.9%).⁹ In SURMOUNT-1, 85% on 5mg, 89% on 10mg and 91% on 15mg lost at least 5%.²

What does this mean for the long term? Larger average loss is not automatically better for every person. The aim of treatment is a sustainable reduction in weight alongside better health, and the dose that gets you there with tolerable side effects is the right one. Trial averages do not predict your own result, and both medicines work alongside a reduced-calorie diet and increased physical activity, not instead of them.²

If you want a deeper walk through how Mounjaro behaves beyond the first year of use, see our guide to the long-term effects of Mounjaro.

06 · Mechanism and ongoing use

How the two mechanisms shape ongoing use

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

This dual action is what distinguishes Mounjaro from single-action GLP-1 medicines such as semaglutide (Wegovy and Ozempic).¹ Both medicines slow stomach emptying, which is why large portions sit heavily.

Both medicines are once-weekly injections. Mounjaro comes as a pre-filled multi-dose KwikPen in six strengths: 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg and 15mg.¹ Wegovy comes as 0.25mg, 0.5mg, 1mg, 1.7mg and 2.4mg pens, stepping up after at least four weeks and reaching the 2.4mg maintenance dose from week 17.¹⁸ Both therefore involve a gradual build-up designed to let your body adjust.

Daily-injection liraglutide (Saxenda) works differently from both. It is supplied at 6mg per millilitre and is injected daily, unlike the once-weekly pens. Your prescriber can advise on whether it is relevant to you.

Finally, never run two GLP-1 medicines together. Mounjaro must not be combined with other GLP-1 medicines, unlicensed "research" peptides, or compounded copies, since these combinations have no safety data and no regulated supply chain.

07 · Side effects over time

Side effects over time: what trials and leaflets tell us

Gut side effects are the main tolerability issue reported for semaglutide 2.4mg. In STEP 1, gastrointestinal side effects were reported by 74.2% of people on semaglutide versus 47.9% on placebo, and 7.0% stopped treatment because of side effects compared with 3.1% on placebo.⁹ Those are trial figures for one medicine, not a comparison with tirzepatide.

Both medicines commonly cause digestive effects, and both are introduced gradually. On Mounjaro, the most common side effects, affecting more than 1 in 10 people, are nausea, diarrhoea, vomiting, constipation and abdominal discomfort.

How do these effects change with time? The dose ladder exists because side effects are most noticeable as you step up. If a dose does not suit you, your prescriber can discuss options rather than leaving you to push through.

Day-to-day habits help. No food is banned on Mounjaro, but many people feel worse after very fatty, fried or very sugary food, and large portions sit heavily because the stomach empties more slowly. Smaller, slower meals work better. Strong coffee on an empty stomach can aggravate nausea or reflux for some people, though there is no interaction between Mounjaro and caffeine.

Two further points relate to the long run. First, alcohol has no direct interaction with Mounjaro, but drinking on a reduced appetite and emptier stomach can hit harder than usual. If you take insulin or a sulfonylurea, alcohol also raises the risk of low blood sugar. Second, new symptoms that are not listed in the leaflet are still worth mentioning to your prescriber, and you can report any suspected side effect through the MHRA Yellow Card scheme.¹⁹

For a focused look at this topic, see our related guide to the long term side effects of these two medicines, and our page on whether Mounjaro can cause long-term effects.

08 · Serious and rare risks

Serious and rare risks to know about

Serious side effects are uncommon, but they need urgent attention. Seek immediate medical help for severe, persistent stomach pain that may spread to your back, with or without vomiting, which may signal pancreatitis.¹ Pain in the upper right abdomen, fever or yellowing of the skin or eyes may signal gallbladder problems, so get medical help straight away. Swelling of the face or throat and difficulty breathing may signal a severe allergic reaction, so get medical help straight away.¹³

Thyroid safety is the question most people raise about long-term use. In rodent studies, tirzepatide caused thyroid C-cell tumours. It is not known whether this applies to humans, and no increase has been shown in human trials.¹ As a precaution, tell your prescriber if you or a close relative have had medullary thyroid cancer or the inherited condition MEN 2. Routine thyroid monitoring is not required for most people.

Kidney problems are rare, and the main route to them is dehydration. Vomiting or diarrhoea can dehydrate you quickly, and reduced appetite means less fluid from food. Keep water within reach through the day, and treat an inability to keep fluids down as a reason to contact your clinical team rather than something to push through.

Who should not take Mounjaro at all? You should not take it if you are allergic to tirzepatide or any of its ingredients, and it should not be used during pregnancy or while trying to conceive.¹ Your prescriber will take extra care, or may recommend against treatment, if you have a history of pancreatitis, severe gut or digestive disease, diabetic retinopathy, or gallbladder problems. Mounjaro must not be used during pregnancy, and it should be stopped at least one month before trying to conceive. If you become pregnant during treatment, stop the medicine and tell your prescriber promptly. If you take insulin or a sulfonylurea alongside Mounjaro, watch for low blood sugar such as shakiness, sweating or confusion, as your prescriber may need to adjust those medicines.

09 · Muscle, protein and nutrition

Muscle, protein and nutrition on long-term treatment

Protecting muscle is one of the most useful things you can do on either medicine. Some of any rapid weight loss comes from lean tissue, and protecting muscle protects your metabolism, strength and appearance. The two levers are adequate protein and resistance exercise two or more times a week. This matters more, not less, as the dose rises and appetite falls.

Aim to include a protein source at every meal. That is harder when appetite is low, so it helps to plan meals rather than eat to hunger. Prioritise protein, vegetables and fibre, and drink regularly. Because the stomach empties more slowly, smaller and slower meals tend to work better than large plates.

Exercise is part of the licence, not an optional extra. Nothing special is required. The evidence-backed pattern is regular moderate activity, such as brisk walking, plus resistance work for muscle. Start where you are and build up. On injection days with early side effects, lighter movement still counts. Exercise also protects against regain if you later stop treatment.

What about vitamins? No supplement is required with Mounjaro, but eating much less can leave gaps, so a standard daily multivitamin is a reasonable safety net while losing weight. Discuss anything beyond that with a pharmacist. Oral supplements, like other oral products, may be absorbed more slowly when you start treatment.

These points apply equally if you are on semaglutide, because both medicines work by reducing appetite and slowing stomach emptying.

Treatment is licensed alongside a reduced-calorie diet, so the aim is a sustainable deficit, not a perfect food list. Alcohol adds calories that work against your goals, though many people find their desire for alcohol drops on treatment. The aim over years is a pattern you can live with, because the medicine supports habits rather than replacing them.

Our companion app, GLPTrackr, is free on iOS and Android and helps you track doses, weight and side effects over time. That record is useful at monthly reviews, when your prescribing team assesses how treatment is going.

10 · Stopping, switching and regain

Stopping, switching and what happens afterwards

Long-term use is a decision you revisit, not a fixed commitment. Tirzepatide has a half-life of about five days, so after a final dose it takes roughly 4 to 5 weeks to clear the system. There is no way to speed this up, and nothing needs doing while it clears.¹

Switching between medicines is a separate decision. There is no licensed direct conversion between semaglutide and tirzepatide. It 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.

Reasons people consider switching from semaglutide to tirzepatide include wanting a larger average effect based on SURMOUNT-5, or finding semaglutide hard to tolerate. Reasons to stay include doing well on the current medicine. Both are legitimate.

Never overlap the two. Running two GLP-1 medicines together has no safety data behind it. Equally, avoid anything that promises faster results outside a licensed pathway, such as unlicensed "research" peptides like retatrutide, which has no UK licence, or compounded copies. That promise is itself the warning sign.

Because Mounjaro slows stomach emptying, it can affect how quickly some oral medicines are absorbed, particularly when you start treatment or increase the dose. Share your full medicine list at every review, including anything you take by mouth. 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.

Finally, if you are unsure whether continuing is right, you do not have to decide alone. Our prescribing team provides monthly reviews, dose titration and follow-up assessments, and repeat orders re-check suitability, with no auto-shipping.

11 · Cost of staying on treatment

What staying on treatment costs over a year

Long-term use is a long-term cost, so plan for a full year. If you step up after 4 weeks on each dose, your first four pens (2.5mg to 10mg) cost £959.96 at standard prices. A first year of 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. These are standard prices before discounts: a new customer's first order is £40 less, and every later order is £25 less.

If you settle at another strength, work from the monthly price instead: £279.99 at 7.5mg, £290.99 at 10mg or £319.99 at 12.5mg per month.

Across the UK pharmacies we track, the cheapest and dearest Mounjaro pen across all doses and providers ranged from £143.96 to £339.00 as of 10 October 2026. Boots' lowest and highest dose prices were £179.00 to £339.00. The gap between providers for the same dose ran from £27 to £41. See our guide to Mounjaro costs for long-term use for planning.

On a first order, a first Mounjaro 2.5mg pen is £129.99 and a first Wegovy pen is £99.99.

What about the NHS? 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, so ask your GP.

If you go private, our service includes a free consultation reviewed by a GPhC-registered prescriber, official LillyDirect supply, free next-day tracked delivery, and ongoing monthly reviews. There are no subscriptions, and Klarna and pay-monthly options are available. Same-day dispatch applies when you order by 3pm. Payment is taken when you place the order; if the prescriber decides the treatment is not suitable, the order is refunded automatically in full.

Obesity itself carries long-term health costs, which is part of why people weigh treatment seriously. Our blog covers the short and long term health risks of obesity.

12 · Alternatives and shortcuts

Tablets, supplements and "natural Ozempic"

The short answer is that nothing sold as a natural GLP-1 equivalent has comparable evidence. Supplements such as berberine 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. They are not substitutes for prescribed treatment.

The phrases "poor man's Ozempic" and "natural Ozempic" refer to those supplements. Dramatic weight-loss claims from sellers are a reason for caution, not reassurance.

What about licensed alternatives? There is no tablet form of Mounjaro, since tirzepatide is injection-only in the UK. Two GLP-1 weight-loss tablets are now licensed: Wegovy tablets (oral semaglutide, from Novo Nordisk), approved by the MHRA in June 2026, and Foundayo (orforglipron, from 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. You can see current Wegovy tablet prices through our weight loss treatments overview.

Other licensed options work differently. Orlistat is a tablet that blocks some dietary fat absorption and produces smaller average losses. Wegovy and Saxenda (liraglutide) are other licensed injectables. Your prescriber can advise on figures and fit.

Which is safer, Ozempic or Mounjaro? For weight loss, the question has a licensing answer. Ozempic is semaglutide licensed for type 2 diabetes, so prescribing it privately for weight loss is off-label. The licensed weight-management options are Mounjaro and Wegovy.¹⁸ A regulated UK pharmacy will not supply Ozempic for weight loss, so the real comparison is Mounjaro versus Wegovy, where SURMOUNT-5 applies.

Anyone offering to supply a prescription injection without a consultation or prescription is a warning sign. Genuine Mounjaro KwikPens from us come via official LillyDirect supply, dispensed by our GPhC-registered pharmacy (registration 9012878). If you spot a suspicious product, report it to the MHRA, which also runs the Yellow Card scheme.⁷