Mounjaro Clinical Trial: What the Research Shows (October 2026)

01 · The core answer

What the Mounjaro clinical trials tell you

Mounjaro (tirzepatide) was tested in a large programme, and the findings that support its UK licence come from randomised trials in adults with obesity and in adults with type 2 diabetes.¹ Mounjaro is the brand name for tirzepatide, a once-weekly injectable prescription medicine made by Eli Lilly. In the UK it is licensed for weight management in adults and for type 2 diabetes.¹

For weight loss, the headline trial is SURMOUNT-1.² 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: individual results vary, and treatment works alongside a reduced-calorie diet and increased physical activity, not instead of them. Trials measured results at 72 weeks, which is why a realistic plan runs over months rather than days.¹

Only SURMOUNT-5 supports a direct tirzepatide-versus-semaglutide comparison. Results from separate trials involve different people, durations and doses, so they should never be set side by side as if they were head to head.¹⁵ Our Mounjaro vs Wegovy trial results guide goes through this fairly.

02 · Your decision

Is this relevant to you, and what next?

If you are an adult considering weight management, the trials matter mainly for two reasons: they set expectations and they explain why the dose ladder is gradual. Everyone starts Mounjaro on 2.5mg once a week. The starting dose is about letting your body adjust, not about weight loss itself.¹

If you want to look at treatment rather than research, the Mounjaro pen page shows the live starter-pen price: the standard price is £169.99 and new customers save £40 on their first order with code FIRST40. See the Mounjaro pen prices and consultation page, or our weight loss clinic overview if you are still comparing options. Every order starts with a free consultation reviewed by a GPhC-registered prescriber.

03 · How to read trial results

How to read Mounjaro trial results

A trial average describes a group, not an individual. In any trial some people lose far more than the average and some lose far less, which is why we say individual results vary. Trial averages do not predict your own result.

Three details change how you should read any headline figure. First, the duration: the weight-management trials measured results at 72 weeks, so a figure quoted without a time point is hard to interpret.¹ Second, the comparison group: a placebo-controlled trial tells you how a medicine performs against no active treatment, while a head-to-head trial tells you how two medicines compare. Third, the population: trial participants are selected, supported and monitored, which may not mirror everyday use.

Treatments in these trials were also used alongside a reduced-calorie diet and increased physical activity, which is how Mounjaro is licensed to be used.

When you see a percentage on a social post or a news story, ask which trial it came from, at what dose and over what time. If the answer is missing, treat the number with caution. For a deeper look at timing, see our page on tirzepatide weight loss in 6 months of trials.

04 · SURMOUNT-1 and 5

SURMOUNT-1 and SURMOUNT-5 explained

SURMOUNT-1 is the pivotal obesity trial for tirzepatide and appears in the New England Journal of Medicine.² Its design tested tirzepatide against placebo and reported results over 72 weeks.¹

SURMOUNT-5 is different. It is the trial that compared tirzepatide directly with injected semaglutide, the active ingredient in Wegovy.¹⁵ That makes it the first large head-to-head trial of the two medicines. In SURMOUNT-5, adults on tirzepatide lost on average 20.2% of body weight over 72 weeks versus 13.7% on semaglutide 2.4mg (Wegovy).¹⁵ Another well-known semaglutide trial is STEP 1, which studied semaglutide against placebo and so cannot be compared directly with SURMOUNT-1.⁹

The practical lesson is that both tirzepatide and semaglutide are effective licensed treatments and that your prescriber, not a headline, should guide the choice. Our Mounjaro vs Wegovy trial page and the wider Mounjaro trial overview expand on this.

05 · How tirzepatide works

Why the trials looked at tirzepatide specifically

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 distinguishes Mounjaro from single-action GLP-1 medicines such as semaglutide (Wegovy/Ozempic).¹ It is the reason researchers have asked whether tirzepatide behaves differently from earlier medicines, and the reason SURMOUNT-5 was run.

Tirzepatide has a half-life of about five days, so after a final dose it takes roughly four to five weeks to clear the system. There is no way to speed this up, and nothing needs doing while it clears.¹

06 · Pace and dosing in trials

What trials mean for your pace and dose

Weight loss on Mounjaro is gradual by design. The first weeks on 2.5mg are an adjustment phase and losses are usually modest. Most measurable progress builds from 5mg onward, month by month.¹

After at least 4 weeks the dose increases to 5mg, and can then step up by 2.5mg at a minimum of 4-week intervals (7.5mg, 10mg, 12.5mg) up to a maximum of 15mg weekly, depending on how you respond and tolerate it. Many people settle at a maintenance dose of 5mg, 10mg or 15mg. Higher is not automatically better, and your prescriber will guide the right pace.¹

Treatment response is reviewed by your prescriber. If you have lost less than 5% of your starting weight after 6 months on the highest dose you can tolerate, your prescriber will discuss whether continuing or stopping is right for you.¹

Early loss includes water weight, so the trend over weeks matters more than any single weigh-in. Mild nausea, altered appetite and tiredness in the first days after each injection are the commonest early effects and usually settle.¹³

07 · Oral GLP-1 trials

Oral tirzepatide and the licensed tablets

There is no tablet form of Mounjaro. Tirzepatide is injection-only in the UK.¹

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. Both are prescription-only.²⁰²¹

In the OASIS 4 trial, adults taking semaglutide 25mg tablets for 64 weeks lost on average 13.6% of their body weight, compared with 2.2% on placebo.²² In the ATTAIN-1 trial of 3,127 adults without type 2 diabetes, people taking the highest dose of orforglipron for 72 weeks lost on average 12.4% of their body weight, compared with 0.9% on placebo; the two lower doses gave 7.8% and 9.3%.²³

No trial has compared Mounjaro directly with either tablet, so these figures should not be set against tirzepatide results as if they were head to head. The practical differences matter as much as the averages: Wegovy tablets need a strict empty-stomach routine every morning, Foundayo has no food or water rules, and Mounjaro needs one injection a week.¹ A prescriber will check which option is suitable for your health, your other medicines and your routine.

For wider context see our guide to a GLP-1 clinical trial.

08 · Research still in progress

Lipedema, Alzheimer's, retatrutide and bimagrumab

Several research areas are not licensed uses of Mounjaro.

Tirzepatide has been discussed in relation to lipedema and Alzheimer's disease. Neither is a licensed use of Mounjaro in the UK. If you have either condition, speak to the clinician who looks after it rather than relying on trial news.

Retatrutide and bimagrumab are medicines in development and are not licensed in the UK. Studies combining or comparing them with tirzepatide are research, not a prescribing option. Anyone offering them for sale outside a trial is not offering a licensed medicine.

The same caution applies to "natural GLP-1" supplements such as berberine. They are not medicines, are not regulated for this use and have no comparable trial evidence.¹ A low-cost supplement with no clinical oversight is not equivalent to a studied, licensed medicine.

Our pages on weight loss injections in trial and the SUMMIT trial of tirzepatide and Mounjaro CVOT trial cover specific research programmes in more depth.

09 · Trials near you

Mounjaro clinical trials near you

EverydayMeds cannot enrol you in a Mounjaro clinical trial. EverydayMeds is a GPhC-registered online pharmacy (GPhC 9012878), not a research site, and we do not recruit for studies.

If you want to take part in research, start with your GP or hospital specialist, who will know of local studies you may qualify for.

If your goal is treatment rather than research, there are two routes. 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.

Our private route starts with a free online consultation and a prescriber review. Payment is taken when you place the order; if the prescriber decides the treatment is not suitable, the order is refunded automatically in full. We supply genuine KwikPens through official LillyDirect supply, with free next-day tracked delivery. See our clinical assessment FAQ for how the review works.

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