Semaglutide: definition, mechanism and what it's actually licensed for in the UK

What exactly does the word 'semaglutide' refer to?

Semaglutide is the international nonproprietary name (INN) (the generic scientific label) for a long-acting analogue of human GLP-1, and our page defining semaglutide unpacks that label in plain terms for anyone who wants a clear starting point. Novo Nordisk developed it by modifying the natural GLP-1 molecule so it resists rapid breakdown by the enzyme DPP-4, giving it a half-life long enough for once-weekly injection or once-daily oral dosing. The backbone of the molecule is close to the human hormone but carries a fatty-acid side chain that binds to albumin in the bloodstream, which is what extends its activity.

When semaglutide reaches its receptors (in the gut, the pancreas and areas of the brain involved in appetite regulation) it triggers insulin release in response to food, suppresses glucagon (which would otherwise raise blood sugar), and sends satiety signals that reduce how much a person wants to eat. It also slows gastric emptying, meaning food moves more slowly from the stomach to the small intestine, which stretches the feeling of fullness further. The combination of these effects, sustained over days rather than hours, is what makes once-weekly dosing clinically practical. For the full story of how the molecule came to exist, our page on who developed semaglutide covers the discovery and trial history in detail.

It is worth being precise: semaglutide is a single molecule. The brand name, strength and formulation determine what the product is licensed to treat. Knowing the INN helps when reading medical literature or comparing products, but the prescriber's assessment (not the molecule name alone) determines whether any of those products is right for a given person.

How does semaglutide differ from the other weight-loss medicines now available in the UK?

The clearest contrast is with tirzepatide, sold in the UK as Mounjaro. Tirzepatide activates two receptors (GIP and GLP-1) whereas semaglutide activates one. That dual action appears to drive greater average weight reduction in head-to-head comparison: the SURMOUNT-5 trial, published in the New England Journal of Medicine in 2025, reported meaningfully larger average weight loss for tirzepatide over semaglutide 2.4 mg across 72 weeks in adults with obesity and no diabetes. The gap narrows with the newer 7.2 mg Wegovy dose (approved by the MHRA for the single-dose pen in April 2026) which produced around 20.7% average loss over 72 weeks in trials, closer to the highest tirzepatide doses.

Semaglutide is also the only GLP-1 medicine approved in the UK in a tablet form for weight management. The Wegovy tablet, approved by the MHRA on 11 June 2026, uses an absorption enhancer called SNAC to allow the molecule to cross the gut lining, making it the first oral GLP-1 medicine licensed in the UK for weight loss. Room-temperature storage and no needles make it meaningfully different for people who find injections a barrier. Our Wegovy overview page covers both the injection and tablet formulations side by side.

Orlistat, the other licensed weight-loss medicine, works entirely differently (blocking fat absorption in the gut rather than acting on appetite via gut hormones) so it is a different class altogether, not a GLP-1 analogue.

Which semaglutide products are licensed in the UK, and for what?

The UK currently has four semaglutide products on the market, and the licensing distinctions matter practically.

Ozempic (weekly injection, 0.5 mg and 1 mg) is licensed for type 2 diabetes. It is not licensed for weight management, and it should never be prescribed or sought for that purpose. The NHS and MHRA have been clear on this point, you can read the NHS semaglutide medicines page for a patient-level summary of the approved uses and the differences between products.

Rybelsus (daily tablet, 3 mg, 7 mg and 14 mg) is also licensed for type 2 diabetes only. Those three tablet strengths are specific to the diabetes product and are entirely separate from the Wegovy tablet schedule.

Wegovy injection (weekly subcutaneous injection, titrated from 0.25 mg up to the standard 2.4 mg maintenance dose and now to 7.2 mg) is licensed for weight management in adults with a BMI of 30 or above, or 27 or above alongside at least one weight-related health condition. NICE has recommended it within NHS specialist weight management services under its appraisal TA875, though access on the NHS involves referral thresholds and waiting lists.

Wegovy tablets (once-daily oral, titrated from 1.5 mg to the 25 mg maintenance dose) carry the same weight-management licence as the injection. Private prescription only at launch; a NICE appraisal would be required before NHS commissioning. If you are thinking about how the costs stack up across private routes, our Wegovy price comparison page sets out the market context honestly. For a broader look at semaglutide's different formulations and what each is approved for, our semaglutide overview is the place to start.

What should people understand about semaglutide before speaking to a prescriber?

A few things come up repeatedly in consultations and are worth understanding clearly in advance. First, these are long-term medicines, not short courses. The weight-loss evidence from trials like STEP 1 (which the NHS semaglutide medicines page references) was generated over 68 weeks, and stopping treatment typically leads to some weight returning over time. Whether continuing indefinitely makes clinical and personal sense is a conversation worth having; our page on long-term Wegovy use addresses what the evidence currently shows.

Second, the most common side effects are gastrointestinal: nausea, loose stools, constipation, indigestion and occasionally vomiting tend to be most noticeable at the start of treatment or after a dose increase, and they often ease as the body adjusts. Rare but serious effects (including acute pancreatitis) warrant urgent medical attention if severe or persistent stomach pain develops, particularly pain that radiates to the back.

Third, eligibility is assessed clinically, not by BMI alone. A BMI figure gives a starting point, but a prescriber weighs up the full picture: other conditions, medicines already being taken, lifestyle factors and medical history. Women taking oral contraceptives should be aware that semaglutide can affect how oral medication is absorbed, particularly early in treatment, this is one of the things a prescriber will want to cover. Anyone pregnant, breastfeeding or trying to conceive should not use semaglutide; under-18s are not covered by the licence either.

Finally, it helps to know that genuinely licensed semaglutide products require a prescription in the UK. Sellers offering them without clinical assessment are operating outside the law, and the MHRA has warned repeatedly about counterfeit products circulating online. Verify any pharmacy you consider using on the GPhC register, it takes about thirty seconds. If a Monday order fits your week best, or you are planning around a bank holiday, knowing the pharmacy's dispatch cut-off in advance matters more than it might seem. At nume, a free clinical consultation is where any conversation about semaglutide begins, reviewed the same working day by a real prescriber, not software.