Semaglutide defined: what it is, how it works, and why it matters for weight management in the UK

Step 1, what semaglutide actually is at a biological level

Your digestive system releases a hormone called GLP-1 (glucagon-like peptide-1) whenever you eat. It tells your brain you have had enough, slows the rate at which food leaves your stomach, and prompts the pancreas to release insulin in response to rising blood sugar. If you want to understand the science precisely, our page covering the semaglutide definition and how the molecule is classified explains this in full. That extended action is why a single weekly dose can keep appetite suppressed across the whole seven-day cycle.

The molecule was developed by Novo Nordisk and belongs to the drug class known as GLP-1 receptor agonists. If you have read about tirzepatide (the active ingredient in Mounjaro) it is worth knowing that semaglutide works on one receptor pathway, while tirzepatide activates two (GLP-1 and GIP). Both are licensed for weight management in the UK, though the clinical evidence and licensed indications differ. You can read a broader overview of semaglutide and its place in UK weight management if you want that comparison in more depth.

One detail that surprises people: because semaglutide mimics a naturally occurring hormone rather than stimulating the central nervous system, people sometimes wonder whether it acts like a stimulant, and you can find a clear answer on our page looking at whether semaglutide is a stimulant. The difference lies in the dose, the licensed indication, and the brand name attached to it, which matters enormously from a regulatory and prescribing standpoint.

Step 2, how the UK licensing divides the brands

A question our prescribers hear most weeks is whether Ozempic and Wegovy are the same thing. The short answer is that both contain semaglutide, but they carry different UK licences. Ozempic is authorised by the MHRA for type 2 diabetes management. Wegovy is authorised for weight management in adults with a BMI of 30 or above, or a BMI of 27 or above alongside at least one weight-related health condition such as high blood pressure, high cholesterol, or obstructive sleep apnoea. Prescribing Ozempic for weight loss would be off-label, that is not what its UK licence covers, and the NHS medicines information for semaglutide makes that distinction clearly.

Wegovy itself has expanded since its original UK launch. The standard maintenance dose of 2.4 mg weekly (reached by titrating up from 0.25 mg over roughly four months) was joined by a higher 7.2 mg dose, approved by the MHRA in January 2026 and, from April 2026, available as a dedicated single-dose pen. Then, on 11 June 2026, the MHRA approved the first oral semaglutide tablet for weight management (also branded Wegovy) making the UK the first country in Europe to licence this form. The tablet follows a separate dose schedule, and if you are weighing up the injection against the tablet, our page on semaglutide 1 mg dosing and how the titration schedule works gives useful context on where that starting point fits. It requires no refrigeration, which many patients find easier to manage day to day.

For a closer look at the injection's trial record, including the weight-loss percentages from the STEP programme, the semaglutide weight-loss percentage page goes through the figures in detail.

Step 3, the practical experience of taking it

Semaglutide works gradually. The starting dose of 0.25 mg (for the injection) or 1.5 mg (for the tablet) is not the dose that produces meaningful weight loss, it exists to let the body adjust, reducing the likelihood of nausea or digestive discomfort in the early weeks. The prescriber then steps the dose up at roughly monthly intervals, and most of the measurable effect on body weight builds over the first six months and beyond.

The most common side effects across the STEP trial programme were gastrointestinal: nausea, loose stools, constipation, and reflux were the most frequently reported. These were generally mild to moderate in severity and tended to settle as the body adapted. Taking the injection with a small meal and staying well hydrated helps many people. The NICE technology appraisal for semaglutide (TA875) notes that if fewer than 5% of body weight has been lost after six months on the maintenance dose, continuing treatment should be reviewed, which is one reason why ongoing clinical oversight matters throughout, not just at the start.

Because the medicine slows gastric emptying, it also affects how other medicines and food are absorbed. People taking oral contraceptives alongside tirzepatide are advised to add a barrier method during dose increases, the evidence for semaglutide is less definitive, but it remains a conversation to have with a prescriber. Storage for the injection is straightforward: refrigerated at 2–8°C, with a limited window at room temperature covered in the patient information leaflet. The tablet requires no refrigeration.

Step 4, what this means if you are considering treatment

Semaglutide is a prescription-only medicine in the UK. That means supply requires a clinical assessment: a prescriber reviews your health history, current medicines, BMI, and any weight-related conditions before deciding whether it is appropriate. NHS access is available via specialist weight management services under NICE criteria, though waiting lists vary considerably. Private routes through a regulated pharmacy offer the same clinical gate without the queue, provided the pharmacy is registered with the GPhC and has a genuine prescribing process in place.

If you are considering private treatment, it is worth looking at what Wegovy costs in the UK and understanding what a legitimate price should include. Cost alone is a poor guide to quality for a prescription medicine; the right question is whether the clinical process behind the price is robust. You can also explore the full range of licensed options on the weight-loss treatment overview.

At nume, every consultation is reviewed by a GPhC-registered Independent Prescriber, a named clinician reads your answers, not an automated system. If you are clinically suitable and would like to proceed, check your eligibility and start your free consultation.