The semaglutide discovery: how a gut hormone became a weight-loss medicine

Step 1: discovering GLP-1, the hormone at the heart of it

The chain of events that produced semaglutide began in 1983, when researchers identified glucagon-like peptide-1 (GLP-1) — a short-lived gut hormone released in response to eating. GLP-1 prompts the pancreas to release insulin, damps down glucagon, slows gastric emptying and, crucially, signals the brain to reduce appetite. It does all of this through dedicated receptors found throughout the gut, pancreas and central nervous system.

The problem was timing. Natural GLP-1 is broken down by an enzyme called DPP-4 within one to two minutes of entering the bloodstream. That is plenty of time to influence digestion after a meal, but far too brief for a therapeutic medicine, no patient could inject a hormone that vanished within seconds of the needle being withdrawn.

The pharmaceutical goal became clear: find or engineer something that activates the same receptor but survives long enough to matter clinically. Novo Nordisk, among others, began pursuing that goal in earnest through the 1990s. Their earlier work led to liraglutide, a once-daily GLP-1 analogue; the full story of that line of research is covered in our look at the development of liraglutide and semaglutide.

Step 2: the Gila monster's unexpected contribution

In 1992 a separate discovery changed the picture. Endocrinologist John Eng, working at the Bronx VA Medical Center, isolated a peptide from the venom of the Gila monster, a large lizard native to the American south-west. The peptide, exendin-4, shared about 53% of its structure with human GLP-1 but was far more resistant to DPP-4 degradation, lasting hours rather than seconds.

Exendin-4 became exenatide, the first GLP-1 receptor agonist approved as a medicine. More importantly, it proved the concept: a molecule built around GLP-1's receptor-binding shape, but chemically hardened against rapid breakdown, could work therapeutically.

Novo Nordisk's chemists took a different approach to durability. Rather than borrowing lizard biology, they modified the human GLP-1 molecule itself. By attaching a long fatty-acid chain to the peptide, they made it bind reversibly to albumin, the most abundant protein in human blood. Albumin acts as a molecular shield, protecting the drug from DPP-4 and the kidneys. The result was a half-life of roughly one week, long enough for a single weekly injection to maintain stable drug levels throughout.

That modification is what semaglutide is. If you are curious about how semaglutide was discovered, including the precise chemical steps that led to the final molecule, that page traces the process in detail. To read more about who specifically is credited with discovering semaglutide, there is a fuller account of the scientists and teams involved.

Step 3: the clinical programme that brought semaglutide to a licensed weight-loss medicine

Semaglutide was initially developed for type 2 diabetes, approved in that indication before anyone had run the large weight-loss trials. A question our prescribers hear most weeks is why the diabetes formulation (Ozempic) and the weight-management one (Wegovy) contain the same molecule but carry different licences. The answer lies in dosing: the weight-management trials used a 2.4mg maintenance dose, roughly double the diabetes maintenance dose, and that higher dose produced substantially greater appetite suppression and weight change.

The pivotal phase 3 evidence came from the STEP programme. STEP 1 (1,961 adults with obesity, 68 weeks, no diabetes) showed an average body-weight reduction of around 15% on semaglutide 2.4mg compared with around 2.4% on placebo, as published in the NEJM STEP 1 paper. That evidence base supported NICE's recommendation of semaglutide for weight management (TA875) and its subsequent licensing as Wegovy in the UK.

Understanding the trial evidence helps explain both the medicine's appeal and its limits, it works for most people who take it consistently, but it is not a substitute for clinical assessment. A prescriber has to determine whether someone is a suitable candidate, which conditions might make it inappropriate, and what monitoring is needed. Details on the eligibility criteria for semaglutide in the UK set out exactly what that assessment involves.

Step 4: semaglutide today, and what the discovery means for patients

The original GLP-1 discovery in the early 1980s took roughly four decades to reach patients as a licensed weekly weight-loss injection. Since then, the science has continued: the MHRA approved a higher 7.2mg Wegovy dose in early 2026, and in June 2026 licensed the first oral GLP-1 medicine for weight management in the UK, a semaglutide tablet. The molecule keeps finding new applications.

For patients, the practical upshot is a medicine with a well-characterised mechanism, a large evidence base, and a clear regulatory history. That history also explains why legitimate access always involves a prescription. The MHRA's oversight of semaglutide (including its Yellow Card pharmacovigilance scheme) is an ongoing part of post-market monitoring, not a one-off approval.

What happened after semaglutide was approved in the UK (including how it is prescribed, what the titration schedule looks like, and what stopping treatment involves) is a different conversation from the discovery story. For a broader picture of the medicine itself, the semaglutide overview covers those practical dimensions. If you are considering treatment and want to understand whether you might be eligible, the free consultation at nume is where that assessment starts, reviewed the same day by a GPhC-registered prescriber. No waiting list, no referral needed.