When Mounjaro Was Created and What That History Means for You

Step 1: The science that made tirzepatide possible

The idea behind tirzepatide starts with two gut hormones: GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide). Researchers had known for years that GLP-1 plays a role in regulating appetite and blood sugar, which is why the first generation of GLP-1 medicines attracted so much interest. GIP had a less obvious story (for a long time its role in appetite regulation was poorly understood) but Eli Lilly's scientists pursued evidence that activating both receptors simultaneously might produce stronger effects than targeting either one alone.

That hypothesis drove Lilly's internal research programme through the 2000s and 2010s. Designing a single molecule capable of binding meaningfully to two distinct receptors, at the right potency and with a manageable safety profile, was not straightforward. Tirzepatide was the compound that eventually cleared those hurdles. You can read more about the people and teams behind that effort on our page about who created Mounjaro.

The NHS medicines page for tirzepatide now summarises how the drug works at a patient level: it slows gastric emptying, increases the sense of fullness and acts on areas of the brain involved in appetite. All of that flows directly from the dual-receptor mechanism Lilly spent years engineering.

Step 2: Clinical trials and the SURMOUNT programme

Before any medicine can be licensed, it must pass through phases of clinical testing — first in small safety studies, then in larger trials designed to establish how well it works and in whom. For tirzepatide, the pivotal phase 3 programme was called SURMOUNT. The first and most widely cited trial, SURMOUNT-1, randomised 2,539 adults with obesity and reported average body-weight reductions of around 20 to 21 per cent at the highest dose over 72 weeks, figures published in the New England Journal of Medicine that formed the core of Lilly's regulatory submissions.

The background on when tirzepatide was created covers the full regulatory timeline in more detail. The short version: the US Food and Drug Administration approved tirzepatide for type 2 diabetes under the brand name Mounjaro in May 2022, which was the first major approval milestone. Weight-management approvals followed, with the UK's MHRA granting a licence for weight management in November 2023, before a comparable US approval for that indication, which came shortly after.

The SURMOUNT programme also produced a head-to-head comparison with semaglutide 2.4mg. In the SURMOUNT-5 trial, published in the New England Journal of Medicine in 2025, tirzepatide produced greater average weight loss than semaglutide 2.4mg over 72 weeks in adults with obesity and without diabetes. That evidence influenced NICE's appraisal process.

Step 3: UK licensing and NICE approval

The MHRA's November 2023 decision to grant Mounjaro a UK weight-management licence was based on the strength of the SURMOUNT data and satisfied itself that the benefit-risk balance was positive. Mounjaro carries a Black Triangle (▼) designation, which means the MHRA actively collects additional safety data post-approval, standard for new medicines, not a sign of concern.

NICE then conducted its own health-technology assessment, weighing clinical evidence against cost-effectiveness for the NHS. That process concluded in December 2024 when NICE published TA1026, recommending tirzepatide for adults with a BMI of 35 or above and at least one weight-related comorbidity, with lower BMI thresholds applying for some ethnic backgrounds. For anyone curious about what those criteria mean in practice, our Mounjaro overview page covers eligibility in full.

NHS rollout is phased (criteria tightened at first and broadening over time) so private prescription through a regulated pharmacy remains the practical route for many people who meet the licensed criteria but not yet the NHS ones. If you want to understand the cost side of that, our Mounjaro cost page sets out what private treatment actually involves.

Step 4: What the creation timeline means for anyone starting treatment now

The gap between early laboratory work and a patient's first pen is usually measured in decades, and tirzepatide is no different. By the time a medicine is licensed in the UK, it has already passed through multiple phases of human testing, international regulatory review and, in this case, a rigorous NICE appraisal. That history is relevant because some people encounter tirzepatide online first and wonder how established it really is.

Diet and lifestyle work alongside the medicine throughout, not as an afterthought. Our page on what to eat when on Mounjaro goes into practical detail, protein intake, hydration and meal timing all matter when appetite is suppressed. Some patients also ask about supplements; the evidence on creatine and Mounjaro is worth reading if muscle maintenance is a concern for you.

The medicine exists because of a long research investment. Using it well requires an equally considered approach to nutrition and clinical oversight. A prescriber can advise on both, which is where a structured consultation, rather than a quick online search, earns its place.

If you'd like to understand more about the clinical team behind prescribing decisions at nume, our clinical team page introduces the people who review every consultation. When you're ready to take the next step, start your free consultation, a GPhC-registered prescriber, not an automated system, reads every application the same day it's submitted.