How Wegovy Works: the biology behind once-weekly semaglutide

You've eaten, so why are you still hungry? Where Wegovy enters the picture

Most people researching Wegovy have spent years doing the right things and still found their hunger relentless. That's not a character flaw; it's biology. Appetite is regulated by hormones, and in people carrying excess weight those signals can be persistently loud. Wegovy addresses that directly.

After a meal, your gut releases GLP-1 (glucagon-like peptide-1) as a natural satiety signal. The problem is that the hormone breaks down within minutes. Semaglutide is a modified version of GLP-1 that survives long enough to act for a full week, binding to the same receptors with a much longer window of effect. The result is that those receptors in the hypothalamus (the brain's hunger-control centre) receive a sustained signal that food has arrived and enough has been eaten.

At the same time, semaglutide slows gastric emptying. Food moves through the stomach more slowly, which extends the physical sensation of fullness after meals and blunts the sharp blood-glucose rises that can drive further cravings. Many people find portion sizes they previously considered tiny start to feel genuinely sufficient. If you want to understand the full mechanism across both GLP-1 pathways, our page on how semaglutide works goes deeper into the pharmacology.

The dose ladder: why treatment starts low and builds slowly

Wegovy is not started at its full maintenance dose. Treatment begins at 0.25 mg weekly, stepping up roughly every four weeks through 0.5 mg, 1.0 mg and 1.7 mg before reaching the 2.4 mg maintenance dose. The MHRA has since approved a higher 7.2 mg dose, initially supplied as three 2.4 mg pens weekly and subsequently as a dedicated single-dose 7.2 mg pen (approved 14 April 2026). The titration schedule is not about building up to a bigger effect gradually; it is about giving your digestive system time to adapt, which is why GI side effects (nausea especially) tend to be most noticeable in the first weeks and ease considerably as the body adjusts.

Your prescriber sets the pace. Skipping rungs, stopping abruptly or adjusting the schedule without clinical input can reintroduce side effects or reduce effectiveness. How quickly weight loss becomes apparent varies between people, but most begin to notice changes in appetite and food intake within the first few weeks of treatment rather than months, and our guide on how soon Wegovy works gives a realistic picture of what that timeline looks like. For a practical sense of what to expect week by week, this page on Wegovy's weekly action explains what is happening at each stage of the cycle.

The starting dose is purely a tolerability measure, the therapeutic work is done at the maintenance level. That distinction matters, because some people worry early on that the medicine is not doing anything. It is. Your system is adjusting.

What the evidence shows, and what Wegovy does not do

The STEP 1 trial, published in the New England Journal of Medicine, followed adults with obesity or overweight plus a weight-related condition for 68 weeks. Those taking 2.4 mg semaglutide lost an average of around 15% of body weight, compared with about 2.4% in the placebo group. That is a clinically meaningful reduction for most people.

The higher 7.2 mg dose narrows the gap with tirzepatide in trials, with reported average weight loss of around 20.7% over 72 weeks. Whether Wegovy works for any individual depends on the full clinical picture, starting weight, other health conditions, how consistently the medicine is used alongside dietary and activity changes. For a plain-language summary of the evidence, the NICE technology appraisal for semaglutide (TA875) sets out what the independent committee found.

Wegovy is not a standalone treatment. Its licence requires it to be used alongside a reduced-calorie diet and increased physical activity. The medicine does not change what you eat; it changes how hungry you feel, which makes changing what you eat substantially easier, and our page on how Wegovy works for weight loss explains why that shift in hunger signalling translates into meaningful results. People who get the most from it tend to use the reduced appetite as a window to build habits that can persist beyond treatment.

Wegovy is not suitable for everyone, and a prescriber decides whether it is appropriate based on your BMI, health history and current medicines. Adults with a BMI of 30 or above, or 27 or above with a qualifying weight-related condition, may be eligible, but that is an outline, not a guarantee. Our page on how well Wegovy works in practice looks at factors that influence individual response. You can also read about the cost of Wegovy in the UK if you are weighing up your options.

If you are curious about whether Wegovy or another licensed treatment might suit your situation, speaking to a prescriber is the logical next step. At nume, every consultation is reviewed the same day by a real GPhC-registered prescriber. Speak to our prescribers and get a clinical view, with no obligation.