Where does semaglutide come from — and why does it matter?

You have this hormone already, semaglutide is built to mimic it

Imagine finishing a meal and feeling that first wave of fullness. A large part of that signal comes from a hormone called GLP-1 (glucagon-like peptide 1) which your small intestine releases almost immediately after food arrives. It tells the pancreas to release insulin, slows the stomach from emptying too quickly, and sends signals to the brain that you have had enough. The sensation is real. The mechanism is older than any medicine.

The problem, from a treatment perspective, is that your body breaks GLP-1 down within minutes. Natural GLP-1 is too short-lived to form the basis of a once-weekly injection. Scientists at Novo Nordisk spent years working out how to extend that window. What they arrived at was semaglutide: a molecule built on the same structural scaffold as GLP-1, but modified at several points so that it binds to albumin (a protein in the blood) and resists the enzymes that would normally dismantle it. The result is a half-life of roughly seven days, which is what makes the weekly dosing schedule possible. The NHS semaglutide medicines page explains this mechanism in clear patient-facing terms.

It is worth pausing here for a moment, because patients sometimes worry that semaglutide is somehow foreign to the body. It is not extracted from an animal or a plant; it is not a hormone stolen from another species. It is a carefully engineered version of something your own gut already makes. That does not mean it is without side effects (the gastrointestinal effects many people experience at the start of treatment are essentially an amplified version of what your gut already does after eating) but it does mean the underlying biology is familiar.

How semaglutide went from a research project to a licensed medicine

Novo Nordisk, the Danish pharmaceutical company, began working on GLP-1-based medicines in the 1990s. The first approved drug in this class was exenatide, a compound derived from a protein found in Gila monster saliva, an interesting piece of pharmacological history, though semaglutide itself has no reptilian ingredient. Novo Nordisk's research programme eventually produced semaglutide, which received its first UK regulatory approval for type 2 diabetes (as Ozempic) before the higher 2.4mg weekly dose was studied specifically for weight management.

The pivotal weight-loss evidence came from the STEP programme of clinical trials. STEP 1, published in the New England Journal of Medicine, randomised over 1,900 adults with obesity and no diabetes; participants on 2.4mg semaglutide lost an average of around 15% of body weight over 68 weeks alongside lifestyle support. Those results underpinned the MHRA's approval of Wegovy for weight management, followed by NICE's recommendation under technology appraisal TA875 for use within specialist weight management services.

If you have been reading about your options and feeling a little lost in the alphabet soup of brand names and trial acronyms, that is entirely understandable. The short version: Ozempic and Wegovy are the same active ingredient at different doses, approved for different conditions. Only Wegovy (injection and, since June 2026, tablet) is licensed in the UK for weight management. Our overview of Ozempic and weight loss explains that distinction clearly.

What the manufacturing origin means for storage, supply and safety

Because semaglutide is a biological medicine produced through genetic engineering, it is sensitive to temperature in a way that a simple chemical tablet is not. The pre-filled Wegovy pen needs to be refrigerated at 2–8°C; the exact window for keeping it at room temperature if refrigeration is temporarily unavailable is set out in the Patient Information Leaflet and should always be the reference point rather than any general rule of thumb. Knowing how to store semaglutide correctly is a practical part of getting the most from your treatment.

The biological manufacturing process also has implications for supply. Semaglutide is not a commodity that can be scaled up overnight in a factory producing simple chemicals; it requires specialist fermentation and purification steps. That is one reason the global surge in demand for GLP-1 medicines led to intermittent supply pressures from 2022 onwards. It is also why the MHRA has repeatedly warned about counterfeit pens circulating online, genuine semaglutide is difficult to produce, and fakes may contain nothing of value or, worse, something harmful. Any legitimate supply comes from the licensed UK supply chain; suspicious offers of semaglutide online without any clinical process attached should be treated as a serious red flag. Report anything suspicious at the MHRA's Yellow Card scheme.

Once you are on treatment, small practical details matter more than most people expect beforehand. Rotating injection sites, for instance, reduces the chance of tissue changes under the skin. Our guide on where to inject semaglutide covers the technique side of things in detail. And if you are curious about what happens to the medicine's effects after treatment ends, the page on coming off semaglutide addresses that honestly.

Private treatment: what clinical review involves and how to approach it

In the UK, Wegovy is a prescription-only medicine. A prescriber (not an automated questionnaire) looks at your answers, your current health picture and your history before deciding whether it is appropriate. At nume, that review is carried out by a GPhC-registered Independent Prescriber on the same day you submit your consultation. There are no waiting lists and no referral letters; you do not need to meet the NHS's phased eligibility criteria, though the private licensed eligibility thresholds still apply.

If you would like to explore whether semaglutide is suitable for you, our weight-loss treatment overview sets out the options, and our frequently asked questions cover the most common practical queries. For context on what private treatment typically costs, the Wegovy prices page walks through what is included in a single transparent price. Our clinical team signs off every consultation personally. When you are ready, you can check your eligibility with a free consultation.