How Wegovy weight loss medication works — and what to expect

Step 1 — what semaglutide actually does in your body

When you inject Wegovy, semaglutide gets to work by binding to GLP-1 receptors distributed across the gut, pancreas and brain. GLP-1 is a hormone your body releases naturally after eating; semaglutide is a synthetic version that stays active far longer. The result is a cascade of signals that slow the rate at which the stomach empties its contents into the small intestine, extend the feeling of fullness after meals and reduce the drive to eat between them.

At the brain level, semaglutide acts on areas involved in appetite and reward, reducing the pull towards high-calorie foods rather than simply making eating feel unpleasant. This is why many people on treatment describe eating less without feeling hungry, rather than feeling as though they are fighting cravings. The biology behind semaglutide's effect on appetite goes into more detail on these pathways if you want a deeper picture.

Because the mechanism works through appetite regulation rather than willpower, the results depend on the dose being sufficient to sustain those signals throughout the week. That is why the titration schedule exists and why stopping treatment typically leads to some weight regain: the hormonal environment shifts back. Understanding this upfront helps set realistic expectations. The clinical overview of how Wegovy works covers the receptor science in full.

Step 2, the titration schedule: why you don't start at the full dose

Wegovy is not a medicine you begin at full strength. The licensed schedule runs 0.25 mg for four weeks, then 0.5 mg, 1.0 mg, 1.7 mg and finally 2.4 mg, each step held for roughly four weeks before the prescriber moves you up. The 0.25 mg starting dose exists purely to let your digestive system adapt; nausea, which is the most commonly reported side effect, is significantly more manageable when the dose increases gradually.

Most weight loss is seen once the maintenance dose of 2.4 mg is reached and sustained, so the early weeks are about building tolerance, not about seeing dramatic results immediately. Some people take longer to tolerate an increase, that is a clinical conversation, not a failure. The MHRA-approved higher dose of 7.2 mg, introduced in early 2026, offers a further step for eligible adults who have already reached 2.4 mg; whether that option suits you is something a prescriber would discuss at review.

Throughout this process, Wegovy is taken alongside a reduced-calorie diet and increased physical activity. The medication supports those changes by managing appetite; it works with the lifestyle plan rather than instead of it. If you have ever wondered where the Wegovy medication name comes from and what it means, that page explains the background in detail. If you are curious about the type of medicine Wegovy is classified as, that page explains the regulatory category in detail.

Step 3, what the evidence shows over time

The STEP 1 trial, published in the New England Journal of Medicine, randomised 1,961 adults with obesity or overweight and at least one weight-related condition. Over 68 weeks, participants on semaglutide 2.4 mg achieved an average body-weight reduction of around 15%, compared with roughly 2.4% on placebo, alongside lifestyle intervention. That figure (roughly one in seven kilograms on average) is the headline the clinical community quotes when comparing GLP-1 options.

Weight loss typically accelerates through months two to six once the maintenance dose is established, then levels off as the body reaches a new equilibrium. Trials show that people who stop treatment tend to regain a significant proportion of lost weight within a year, which is why NICE's recommendation for semaglutide under TA875 frames it as a time-limited treatment of up to two years within a specialist weight management service, an important consideration for anyone planning their longer-term approach. For a broader look at where semaglutide sits as a medicine, the overview page covers its licensed uses across indications.

One everyday habit that helps in practice: many people find it easiest to set a regular day and time for each injection (a Tuesday morning after breakfast, say) so the routine becomes automatic rather than something to remember under pressure. That kind of consistency matters because the weekly dosing interval is part of how the sustained plasma levels are maintained.

Side effects to know about, and when to get medical help

The most common side effects are gastrointestinal: nausea, vomiting, diarrhoea, constipation, indigestion and burping. These are most pronounced after the first injection and after each dose increase, and they usually ease within days to two weeks as the body adjusts. Staying well hydrated and avoiding very large or very fatty meals helps most people manage this phase without significant difficulty.

A smaller proportion of people experience fatigue, headache, dizziness or injection-site reactions. These are documented in the NHS medicines page for semaglutide alongside a full list of less common effects. Serious side effects are uncommon but should be taken seriously. Seek urgent medical attention for severe, persistent stomach pain that may spread to the back (with or without vomiting) as this can be a sign of pancreatitis. Gallbladder symptoms, signs of a serious allergic reaction, and symptoms of significant dehydration following prolonged vomiting or diarrhoea also warrant prompt medical advice.

Any suspected side effect can be reported via the MHRA's Yellow Card scheme, which is how post-market safety data is gathered for Black Triangle medicines like Wegovy. If you have questions about whether Wegovy might suit your circumstances, our prescribers review consultations the same day. You can check your eligibility to start that conversation at no cost.