How Wegovy Works: the jobs semaglutide does inside your body

Step 1: the GLP-1 signal and what it triggers

After you eat, your gut releases a hormone called GLP-1 (glucagon-like peptide-1). It tells the brain you have had enough, it slows the movement of food through the stomach, and it nudges the pancreas to respond appropriately to glucose. In people carrying excess weight, this signalling is often blunted or short-lived. Semaglutide (the active ingredient in Wegovy) is a GLP-1 receptor agonist, meaning it attaches to the same receptors that natural GLP-1 uses and activates them more persistently.

The once-weekly injection sustains that signal continuously rather than in the brief spike that follows a meal. Practically, that translates to feeling fuller on smaller portions, feeling less preoccupied with food between meals, and having a reduced urge to eat past the point of comfort. This is not willpower engineered into a syringe, it is a biological correction to a hormone pathway that, in many people, was genuinely not working as it should. You can read more about how GLP-1 medicines work in general on our semaglutide overview page.

The NHS notes these mechanisms on its tirzepatide and semaglutide medicines pages, and the same GLP-1 pathway underpins the NICE appraisal evidence for Wegovy's use in weight management. Understanding this first step matters because it explains why the dose is introduced slowly: activating GLP-1 receptors strongly from day one tends to cause nausea, so the starter doses exist to let your digestive system adjust before the therapeutic dose is reached.

Step 2: the titration schedule, why the dose climbs in stages

A common misconception is that a lower dose simply means weaker treatment, and that higher is always better from the start. That is not how Wegovy is designed. The titration schedule (starting at 0.25 mg, moving through 0.5 mg, 1.0 mg and 1.7 mg before reaching the 2.4 mg maintenance dose) is built around tolerability, not caution for its own sake.

Each step typically lasts around four weeks. Moving too quickly tends to amplify the gastrointestinal side effects that many people notice early on: nausea, loose stools, or a general feeling of unsettled digestion. Most of these settle as the body adjusts. By the time you reach 2.4 mg, your system has had months to acclimatise, and most people find the maintenance dose far easier to tolerate than they feared the lower doses might suggest.

Your prescriber sets and reviews this schedule, it is not something to adjust unilaterally. If a dose increase is causing persistent symptoms, that conversation belongs with your clinical team, not a forum. Details of the UK-licensed titration steps are published in the Wegovy patient information leaflet on the Electronic Medicines Compendium (eMC). The 2.4 mg target remains the evidence-based maintenance dose for weight management in UK-licensed use, though the MHRA approved a higher 7.2 mg pen in April 2026 for eligible adults, and if you are already familiar with the earlier steps you may find it helpful to read about the Wegovy 0.5 mg dose before discussing whether a higher dose is relevant to your situation with your prescriber.

Step 3: what Wegovy does to weight over time (and what it does not do alone

The STEP 1 trial) 68 weeks of treatment in adults with obesity or overweight plus at least one weight-related condition, no diabetes, recorded an average body-weight reduction of around 15% in the semaglutide group, compared to around 2.4% in the placebo group. Both groups received lifestyle support alongside treatment. That context matters: Wegovy's licence specifies use alongside a reduced-calorie diet and increased physical activity, and that is not regulatory boilerplate. The medicine makes the behavioural changes easier by reducing appetite and food preoccupation, but the food choices and activity still do their part.

Over the months of treatment, people typically notice changes in food preferences as well as portion sizes, some foods that previously felt irresistible become easier to leave. Weight loss is usually gradual and non-linear; weeks where the scale moves little are common and expected. If you are thinking about whether Wegovy or an alternative might suit your situation, our free consultation is the place to have that conversation with a prescriber rather than guessing from a comparison table.

For context on what different weight-loss treatment options look like side by side, the weight-loss treatments overview gives a practical starting point. And if you are curious how Wegovy compares at different stages (including the 1 mg and 2 mg steps) the 0.25–0.5 mg information page and the 1 mg dose page cover those phases in more detail.

Eligibility, safety signals, and who it is not for

Wegovy is licensed in the UK for adults with a BMI of 30 or above, or 27 to 29.9 alongside at least one weight-related condition such as hypertension, type 2 diabetes, high cholesterol, or obstructive sleep apnoea. Lower BMI thresholds may apply for some ethnic backgrounds under UK clinical guidance. BMI alone does not determine suitability, a prescriber weighs your medical history, current medicines, and other factors before recommending it.

The most commonly reported side effects are gastrointestinal: nausea is the most frequent, followed by constipation, diarrhoea, vomiting, and indigestion. These are typically at their most noticeable after starting or increasing the dose and tend to ease within a week or two. Pancreatitis is a rarer but more serious risk, the MHRA issued a Drug Safety Update in January 2026 reminding patients and prescribers to seek urgent help for severe stomach pain that radiates to the back. Wegovy is not recommended in pregnancy, during breastfeeding, or for anyone trying to conceive. It is not licensed for under-18s. Anyone with a history of medullary thyroid carcinoma or MEN2 should discuss this with their prescriber before starting.

For questions specific to how Wegovy interacts with conditions such as irritable bowel syndrome, the Wegovy and IBS page addresses that directly. If you want to understand the full picture of what treatment at nume involves (including identity checks, how prescriptions are reviewed, and what aftercare looks like) about us sets it out plainly. Speak to our prescribers if you are ready to find out whether Wegovy is right for you.