Mounjaro Data: What the Tirzepatide Evidence Shows (October 2026)

01 · The core answer

What does the Mounjaro data actually show?

The main evidence for weight management is the SURMOUNT-1 trial. In the SURMOUNT-1 trial of 2,539 adults, people taking tirzepatide alongside diet and exercise lost on average 15% of their 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

These are group averages, and the comparison group made lifestyle changes without the medicine. Some people in the trial lost more than the average and some lost less. Treatment works alongside a reduced-calorie diet and increased physical activity, not instead of them.²

For a deeper tour of the studies, see our Mounjaro evidence and research data page.

02 · Your decision

Is this data relevant to you, and what next?

The data are most relevant if you are an adult living with overweight or obesity and have tried lifestyle changes on their own. Mounjaro is a prescription-only medicine, supplied only after an online consultation reviewed by a GPhC-registered prescriber. Whether the trial results apply to you depends on your health history, other medicines and goals, which the prescriber assesses.

If you decide to explore treatment, our weight loss clinic explains the pathway. You can also see current prices on the Mounjaro pen page: the starter pen is £169.99 at standard price, and a new customer's first 2.5mg pen costs £129.99 with code FIRST40. Prices checked 10 October 2026.

03 · SURMOUNT-1 results

SURMOUNT-1: the headline weight-loss figures

SURMOUNT-1 is the trial behind most of the Mounjaro weight data you see quoted online.

In the SURMOUNT-1 trial of 2,539 adults, people taking tirzepatide alongside diet and exercise lost on average 15% of their 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 These are trial averages, and individual results vary.

The trial also reported how many people reached particular thresholds. 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% of their body weight.²

A worked example helps. For someone starting at 100 kg, 20.9% is about 21 kg. That is straight arithmetic on the trial average, not a promise about what you will lose, and it says nothing about how quickly any individual reaches it.

Notice what the data do not say. They do not say everyone responds equally, they do not say weight stays off if treatment stops, and they do not replace the role of diet and activity. Treat the numbers as a realistic picture of what a group can achieve under trial conditions.

04 · How tirzepatide works

How tirzepatide works: the mechanism data

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. This dual action is what distinguishes Mounjaro from single-action GLP-1 medicines such as semaglutide (Wegovy/Ozempic).¹

Semaglutide's data come from separate trials, so its numbers should not be set beside Mounjaro's as though they came from one study.

Mounjaro comes as a pre-filled multi-dose pen (KwikPen) in six strengths: 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg and 15mg.¹ Doses are stepped up over time under prescriber supervision, which is why the trial results are reported by dose.

05 · The data sheet

Mounjaro data sheet: where to find the official one

The official Mounjaro data sheet is the Summary of Product Characteristics (SmPC), published on the electronic medicines compendium.¹ It is written for healthcare professionals and sets out the licensed uses, dosing, warnings, interactions and storage requirements.

The companion document for patients is the patient information leaflet, also on the compendium and supplied inside the pack.¹³ It covers how to use the pen, possible side effects and what to do if something goes wrong.

Both documents are the authority. Where a blog, social post or product page, including ours, differs from them, trust the SmPC and leaflet. We also keep a plain-English Mounjaro information sheet that summarises the essentials in a more readable form.

A few practical points drawn from the product information. In the UK, a KwikPen in use is licensed for up to 30 days (not above 30°C) out of the fridge. Unopened pens are stored in the fridge until first use and keep until the printed expiry date. For any other storage question, read the leaflet and ask your pharmacy.¹³

06 · Reading trial data

How to read trial data without being misled

Trial data answer a narrow question: what happened to a group of volunteers under set conditions. They are reliable for that and much weaker as a forecast for one person.

First, look at the comparison group. SURMOUNT-1 compared tirzepatide with lifestyle changes alone, so its results show the added effect of the medicine on top of diet and activity.²

Second, check the duration. The SURMOUNT-1 weight figures are for 72 weeks. A different trial may run for a shorter or longer period, so numbers from separate studies should not be set beside each other as if they were measured the same way.

Third, remember averages hide spread. Trial averages do not predict your own result. Age, starting weight, other medicines, adherence to the dose schedule and lifestyle all play a part.

Fourth, be wary of direct comparisons between medicines. Only the SURMOUNT-5 trial supports a head-to-head statement about tirzepatide and semaglutide, so claims that one "beats" the other based on separate trials are not sound.¹⁵

Finally, beware of figures without a trial name. Dramatic weight-loss claims on social media rarely tell you the dose, the duration or the comparison group, which makes them close to useless.

07 · Safety and reporting

Safety data and how to report a side effect

The full list of side effects, warnings and interactions sits in the SmPC and the patient information leaflet, and those are the documents to read before starting treatment.¹ Your prescriber will go through them with you. Serious side effects are uncommon but need urgent attention: for severe, persistent stomach pain that may spread to your back, with or without vomiting, pain in the upper right abdomen with fever or yellowing of the skin or eyes, or signs of a severe allergic reaction, get medical help straight away.

If you notice a new symptom while using Mounjaro, speak to your prescriber. You can also report suspected side effects through the MHRA Yellow Card scheme.¹⁹ A report is a signal for regulators to review, not proof that the medicine caused the problem.

Counterfeit pens are a separate safety issue. The MHRA publishes counterfeit medicine alerts, and you should only buy from a registered pharmacy that you can look up on the GPhC register.⁷ We are GPhC-registered (9012878) and supply genuine KwikPens through official LillyDirect supply. Be wary of anyone offering to supply without a consultation or prescription.

08 · UK licence and NHS data

UK licensing and NHS access

In the UK, Mounjaro is licensed for weight management in adults and for type 2 diabetes.¹ The UK regulator is the MHRA.

On NHS access, 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. Your GP is the right first conversation if you want to know where you stand locally.

09 · Other GLP-1 medicines

GLP-1 data beyond Mounjaro

Mounjaro is not the only licensed option. Wegovy (semaglutide) is a once-weekly injection with its own dose ladder: 0.25mg, 0.5mg, 1mg, 1.7mg and 2.4mg, stepping up after at least four weeks and reaching the 2.4mg maintenance dose from week 17.¹⁸ You can see our Wegovy pen page for current details.

Liraglutide (Saxenda, and products such as Erly) is supplied at a concentration of 6mg per millilitre and is a daily injection, unlike once-weekly Mounjaro and Wegovy.

Licensed tablet options also exist, including Wegovy tablets and Foundayo. Their data come from their own trials and product information, so their results should not be set against Mounjaro's as if head to head. If you are curious about one of them, our blog on Foundayo and what its safety data shows is a good starting point, and your prescriber can advise on which licensed medicine suits you.

The practical point is that each medicine has its own data sheet, dose schedule and evidence base. Compare like with like, and only rely on a head-to-head trial when you want to say one performed better than another.

10 · Supplements and dupes

What about "natural Ozempic" and dupes?

There is no natural version of Mounjaro or Ozempic. Terms such as "poor man's Ozempic" and "nature's Ozempic" are marketing labels for low-cost supplements sold without clinical oversight, and they are not licensed medicines.

The data picture is stark. Trials like SURMOUNT-1 tested tirzepatide, not supplements, and nothing in them applies to a capsule bought online.

Nor can you mimic the effect with food. A reduced-calorie diet and more activity are part of treatment, and they matter, but the medicine's action on gut-hormone receptors is not something a food or powder reproduces.

The same applies to so-called copies. If you are wondering about a Mounjaro dupe or a Mounjaro biosimilar, read our guides first; products that are not the licensed medicine have no SmPC and no regulatory safety data behind them.

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