Your semaglutide guide: the facts behind the medicine

How does semaglutide actually reduce body weight?

GLP-1 (glucagon-like peptide-1) is a hormone your gut releases naturally after you eat. Semaglutide is a synthetic version designed to last much longer in the body, which is what makes once-weekly dosing possible. By activating the GLP-1 receptor, it signals to your brain that you are full sooner and for longer, slows the rate at which your stomach empties, and reduces the drive to eat between meals. The result, for most people, is a sustained reduction in calorie intake without the conscious effort of restriction.

One misconception worth setting aside gently: semaglutide does not burn fat directly. It does not raise your metabolism or suppress hunger through stimulant pathways. The weight loss happens because appetite falls, food intake drops, and the calorie deficit adds up over months. The NHS medicines page for semaglutide explains the mechanism in plain language and is worth reading alongside this guide. For a broader look at the clinical picture, the semaglutide overview on our site covers the full evidence base.

This single-pathway mechanism is also what distinguishes semaglutide from tirzepatide, which acts on two receptors. Neither is inherently better for every person, the right medicine depends on your health history, preferences and what a prescriber concludes after assessing you properly.

Who does the UK licence cover, and what does NHS access look like?

The UK licence for Wegovy covers adults with a BMI of 30 or above, or a BMI of 27 to 29.9 combined with at least one weight-related condition. Conditions that count include type 2 diabetes, high blood pressure, high cholesterol, obstructive sleep apnoea and cardiovascular disease. Lower BMI thresholds apply for some ethnic backgrounds under UK clinical guidance, your prescriber will apply the correct threshold for you.

NICE recommends semaglutide for weight management (guidance TA875) specifically within a specialist weight management service, for a maximum of two years, and only where the 5% weight-loss threshold is met at six months on the maintenance dose. That recommendation shapes NHS access rather than private prescribing, but it gives a useful picture of how commissioners assess the evidence. Waiting lists for NHS specialist services are commonly long in most areas. If you want to understand the full Wegovy access picture (NHS, private and the criteria that apply to each) that page covers it in detail.

Private eligibility follows the licensed criteria: BMI and health history assessed by a prescriber. BMI alone does not guarantee approval; a clinician reviews the whole picture before any decision is made.

What does the trial evidence say about results?

The main evidence base for semaglutide 2.4 mg at the standard maintenance dose comes from the STEP programme. STEP 1, published in the New England Journal of Medicine, enrolled 1,961 adults with obesity or overweight plus a weight-related condition and ran for 68 weeks. Average weight reduction was around 15% in the semaglutide group, compared with about 2.4% for placebo. Participants also received behavioural support, which is part of how the trial was designed.

A higher 7.2 mg dose was approved by the MHRA in January 2026, initially delivered as three 2.4 mg pens weekly and then via a dedicated single-dose 7.2 mg pen approved in April 2026. Trials at that dose reported average weight loss of around 20.7% over 72 weeks, approaching the results seen with higher tirzepatide doses. The dosing guide on our site explains the titration schedule from 0.25 mg upward, which is prescribed and supervised throughout; this is not a medicine you self-titrate.

If you are trying to compare semaglutide and tirzepatide side by side, the UK prescribing guidelines page sets out the regulatory context for both. Which suits you is a clinical question, not a ranking exercise.

What side effects should you know about before starting?

Gastrointestinal effects are the most commonly reported: nausea, loose stools, constipation, reflux and burping. They tend to be most noticeable in the first days after a dose or a dose increase, and most people find they settle within a couple of weeks as the body adjusts. Eating smaller portions, avoiding very fatty meals and staying well hydrated all help. Fatigue, headaches and injection-site reactions are also reported.

The MHRA issued a Drug Safety Update in January 2026 highlighting acute pancreatitis as an infrequent but serious risk with GLP-1 medicines. The symptom to watch for is severe stomach pain that radiates to the back, with or without vomiting, seek urgent medical attention if that happens. You can report any suspected side effects, or a suspect seller, through the MHRA Yellow Card scheme.

Semaglutide is not recommended during pregnancy, whilst breastfeeding, or for anyone trying to conceive. It is not licensed for under-18s. For practical questions about travelling with your pens or what to do at airport security, the Wegovy travel page has specific advice. If you have already been prescribed semaglutide elsewhere and want to understand your ongoing care options, the user guide covers day-to-day management. Our weight-loss treatment overview is a good starting point if you are still deciding which path to take.

A prescriber at nume personally reviews every consultation the same day, a real clinician reads your answers, not software. If semaglutide is right for you and you order before 12pm on a working day, treatment is dispatched the same day and arrives free via tracked DPD the next working day. When you're ready, start your free consultation and our clinical team will take it from there.