How Long Has Mounjaro Been Tested — and What Did the Trials Find?

How long the SURMOUNT trials actually ran — and why 72 weeks matters

When people ask how long Mounjaro has been tested, they usually mean two separate things: how many years the medicine has been in development, and how long individual participants were studied. Both questions have clear answers.

Tirzepatide's phase 3 programme for weight management (the SURMOUNT trials) began in the early 2020s, with the landmark SURMOUNT-1 study publishing results in 2022. That trial followed 2,539 adults with obesity (but without type 2 diabetes) for 72 weeks. Seventy-two weeks is a deliberate choice; short trials can show early weight loss that rebounds once participants stop. Regulators and NICE want to see what happens over a sustained period, which is why 72 weeks became the benchmark.

At the 15mg dose, participants in SURMOUNT-1 lost an average of around 20 to 21 percent of their body weight over that period, figures published directly in the SURMOUNT-1 trial paper in the New England Journal of Medicine. Those are averages across a large group, not a guaranteed individual outcome, and results varied. Still, the scale of the evidence is what allowed regulators to act.

If you want to understand how this timeline connects to when the medicine first appeared in clinics, the history of how long Mounjaro has been used covers the regulatory journey from trials to licensed product.

From weight loss to cardiovascular health: the widening evidence base

SURMOUNT-1 was not the end. The programme extended to several further trials, each answering a different question. SURMOUNT-2 looked at adults who also had type 2 diabetes. SURMOUNT-3 and SURMOUNT-4 examined what happens after a lead-in period on lifestyle intervention, and whether the weight lost with tirzepatide is maintained once treatment stops. Each ran for 72 weeks or longer.

Then came SURMOUNT-5, published in the New England Journal of Medicine in 2025. This was the first direct, head-to-head comparison of tirzepatide with semaglutide 2.4mg in 751 adults with obesity. It found that tirzepatide produced greater average weight reduction over 72 weeks. That single trial matters because much of the earlier evidence relied on indirect comparison across separate studies, SURMOUNT-5 removed that limitation.

Alongside the weight trials, tirzepatide's SURPASS programme studied it in type 2 diabetes across multiple large trials. When you add the SURPASS and SURMOUNT datasets together, the overall tirzepatide clinical programme involved well over 10,000 participants. That cumulative record is what NICE assessed in its TA1026 appraisal of tirzepatide, published in December 2024.

For a sense of how tirzepatide's testing history compares with that of older GLP-1 medicines, the page on how long tirzepatide has been used sets the broader context.

What the evidence does and does not guarantee

Clinical trials measure averages in carefully selected populations under controlled conditions. SURMOUNT-1's participants followed a reduced-calorie diet and increased physical activity alongside treatment, the medicine was tested as part of a combined approach, and UK licensing reflects that. Mounjaro is licensed for weight management alongside dietary changes and increased activity, not as a standalone fix.

The 20 to 21 percent average weight loss figure from SURMOUNT-1 is genuine and well-documented. It is also an average across thousands of people, some of whom lost considerably more and some considerably less. Side effects were common in the trials, predominantly gastrointestinal (nausea, diarrhoea, constipation and indigestion being the most frequent) and were typically most noticeable after starting or after a dose increase. If you are curious about how long Mounjaro has been around, that background helps explain why the monitoring requirements were shaped the way they were. Mounjaro carries a Black Triangle (▼) designation from the MHRA, meaning the medicine is still under additional monitoring, even after approval. That is not unusual for recently licensed products; it is how post-market safety data continues to be collected.

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The trials also inform who the medicine is licensed for. Private eligibility broadly covers adults with a BMI of 30 or above, or 27 or above with at least one weight-related condition such as high blood pressure, high cholesterol or type 2 diabetes. Lower BMI thresholds may apply for some ethnic backgrounds under UK guidance. A prescriber assesses the full clinical picture, because BMI alone never tells the whole story.

If you are trying to understand how quickly results typically appear once treatment starts, the page on how long Mounjaro takes to work covers what the evidence says about early versus longer-term changes. And if cost is part of your thinking, our Mounjaro cost and pricing guide explains what makes up a legitimate private price. For those who want a fuller picture of the commercial and regulatory timeline, the page on how long Mounjaro has been on the market traces the journey from first authorisation to wider availability.

Mounjaro is a prescription-only medicine. A named prescriber (not software) reviews every consultation at nume before any treatment is confirmed. If you would like to explore whether treatment is right for you, you are welcome to check your eligibility with our clinical team.