How Wegovy works: the science behind weekly semaglutide

What GLP-1 is, and why semaglutide borrows its signals

GLP-1 stands for glucagon-like peptide-1, a hormone released by cells in your small intestine when food arrives. Its job is to tell the brain you have eaten and to slow the pace at which your stomach empties. The trouble is that natural GLP-1 breaks down in the bloodstream within minutes, so its influence fades quickly.

Semaglutide is engineered to bind to the same receptor but resist rapid breakdown, staying active for roughly seven days. That sustained signal changes how hunger and fullness register across an entire week, not just in the hour after a meal. The NHS overview of semaglutide explains this mechanism in plain terms on the NHS medicines page for semaglutide.

Because the action is rooted in your own hormonal signalling rather than stimulants or appetite-suppressing chemicals, many people describe the effect as a quietening of food noise rather than a dramatic forced suppression. That distinction matters for understanding what to expect day to day. For a deeper look at the physiology involved, the page on how Wegovy works in the body covers the receptor biology in more detail, and if you want to understand how Wegovy works as a weight loss medication, that guide brings together the clinical picture in an accessible way.

How semaglutide produces weight loss over time

The evidence base for how semaglutide works for weight loss is substantial. STEP 1 (the pivotal phase 3 trial) randomised 1,961 adults with obesity or overweight plus at least one weight-related condition to either semaglutide 2.4 mg weekly or placebo, alongside lifestyle counselling. After 68 weeks, those on semaglutide had lost an average of around 14.9% of body weight versus 2.4% with placebo. More than 86% of participants on semaglutide achieved at least 5% weight loss.

The mechanism behind those numbers involves several overlapping effects. Gastric emptying slows, so a smaller portion creates prolonged fullness. Appetite signals to the hypothalamus are dampened, reducing the impulse to seek food between meals. And resting energy intake tends to fall because appetite itself is genuinely lower, not just consciously restrained.

It is worth noting that semaglutide works alongside (not instead of) a reduced-calorie diet and regular activity. The trial design required lifestyle intervention in both groups; the medicine amplified the results. On its own, without those lifestyle inputs, effects are smaller. If you are thinking about what the treatment journey typically involves, how semaglutide works for weight loss explores the practical side of that process.

If you are weighing up costs alongside clinical factors, the Wegovy prices page sets out what private treatment typically involves in the UK.

The dose schedule and why it starts low

One question our prescribers hear regularly is why Wegovy begins at 0.25 mg when the maintenance dose is so much higher. The answer is straightforward: the opening doses are not designed to produce weight loss. Their purpose is to let your digestive system adjust gradually, keeping nausea and gastrointestinal side effects manageable.

The standard titration moves from 0.25 mg to 0.5 mg, then 1.0 mg, 1.7 mg and finally 2.4 mg, spending roughly four weeks at each level. In April 2026 the MHRA approved a dedicated single-dose 7.2 mg pen for adults with a BMI of 30 or above (the first regulatory approval of this kind in the UK) extending the maximum available dose further. Trials at 7.2 mg reported average weight loss of around 20.7% over 72 weeks, approaching the results seen with tirzepatide at higher doses. The MHRA's announcement on GOV.UK sets out the details of that approval.

Your prescriber determines the pace of titration based on how you tolerate each dose. Rushing up the schedule does not produce faster results and tends to worsen side effects. The page on when Wegovy starts working is a useful companion read if you are wondering what to expect during the early weeks.

Who Wegovy is licensed for, and what that means in practice

Wegovy holds a UK marketing authorisation for weight management in adults with a BMI of 30 or above, or a BMI of 27 to 29.9 alongside at least one weight-related condition such as high blood pressure, high cholesterol or obstructive sleep apnoea. Lower BMI thresholds apply for some ethnic backgrounds under UK clinical guidance. It is not licensed for people under 18, and it is not recommended during pregnancy, breastfeeding or when actively trying to conceive.

NICE recommends semaglutide injection for weight management within specialist services under specific criteria, including a maximum treatment duration of two years (NICE TA875). Private prescribing through a regulated pharmacy operates under the medicine's licensed indications, which is broader than the NHS commissioning criteria. A prescriber assesses the full clinical picture (not BMI alone) before deciding suitability.

Ozempic is also semaglutide but carries a different licence: it is approved for type 2 diabetes, not weight management, and should not be sought for weight loss. The semaglutide overview page covers the difference between these products clearly. For a broader look at the licensed weight-loss options available through a UK online pharmacy, the weight-loss treatments page is the right starting point if you are considering next steps.