What to expect at 4 weeks on Wegovy

What the STEP 1 data tells us about this point in treatment

The STEP 1 trial, published in the New England Journal of Medicine, remains the clearest evidence base for what Wegovy does over time. Week four falls during the dose-escalation phase, before participants reached the 2.4mg maintenance dose that drove the headline results. This matters because semaglutide's weight-loss effect is dose-dependent: appetite suppression deepens as the dose rises, and the body's response to the GLP-1 receptor pathway strengthens accordingly.

In practical terms, this means week four is rarely the moment of dramatic change. Most people at this stage report noticing that they feel full sooner at meals, or that the pull toward snacking has softened. These are signals that the medicine is working as intended (recalibrating appetite-signalling hormones) even when the number on the scales hasn't shifted much yet. If you're comparing notes with someone further along, our overview of what eight weeks on Wegovy tends to look like gives a useful longer view.

One thing the trial data make clear: early non-response on the scales does not predict eventual outcome. Participants who saw modest losses in the first month went on to achieve substantial reductions once they reached and maintained the higher doses. Patience at this stage is, genuinely, evidence-based advice.

Side effects at week four: what's normal, what needs attention

The NHS medicines page for semaglutide lists the most common early effects: nausea, vomiting, diarrhoea, constipation, indigestion, burping and fatigue. At week four (typically the transition from 0.25mg to 0.5mg) GI effects can resurface briefly as the body adjusts to the new dose level. This is expected and, for most people, settles within a week or two.

Practical habits that tend to help: eating smaller portions slowly, avoiding fatty or very rich foods, staying well hydrated, and not lying down immediately after meals. None of these are cures, but they reduce the friction while the dose settles.

Two symptoms warrant prompt medical attention at any point during treatment. Severe, persistent stomach pain (especially if it spreads toward the back) should be assessed urgently, as pancreatitis is a known but infrequent side effect flagged in MHRA guidance. Symptoms of an allergic reaction, including swelling of the face or difficulty breathing, need emergency care. Everything else in the GI category is worth discussing with your prescriber at the next review, but doesn't usually require urgent action. If you have questions between doses, you can always reach the aftercare team.

Appetite changes: what's actually happening physiologically

Semaglutide works by activating GLP-1 receptors in the gut and brain. Gastric emptying slows, so food stays in the stomach longer. Satiety signals reach the brain earlier in a meal. And the reward value of high-calorie foods tends to diminish, many people describe finding it easier to leave food on the plate, or simply forgetting to feel hungry between meals. These effects build as the dose increases, which is why week four is often described as the beginning of appetite change rather than its peak.

For some people the shift feels dramatic from the first week, and if that matches your experience, our account of what the second week on Wegovy is typically like puts those early changes in context. For others it's subtle until the 1mg or 1.7mg stage. Both patterns appear in clinical practice; neither predicts who will lose more weight in the end. If you want to understand how the medicine compares to tirzepatide in terms of mechanism and trial results, our semaglutide overview covers the pharmacology in more depth.

One thing that often catches people out: because appetite falls, total food intake drops, and with it, the risk of low protein and micronutrient intake. Keeping protein adequate (prioritising it at every meal), eating plenty of vegetables, and staying hydrated all matter more than they might have before. A prescriber or dietitian can help you structure this; it's a question our clinical team hears regularly in the first month. The Wegovy weight-loss treatment overview sets out what a full programme of support can look like alongside the medicine.

Should you expect to see weight loss by week four?

Some people do. A reduction of 1–3 kg in the first month is plausible, particularly for those who were already eating less in response to reduced appetite. Others see very little movement at this stage, especially if fluid shifts or changes to digestion are masking fat loss on the scales. Both are consistent with the clinical evidence.

What matters more than the four-week figure is the trajectory. If you're tolerating the medicine, noticing appetite changes and managing side effects, the physiological groundwork is being laid. The steeper losses in the trial cohort came at higher doses, later in treatment, typically from months three or four onward. If you're curious how the picture develops, our guide to what week three on Wegovy tends to bring and then reading about the six-week stage gives a sense of what comes next.

Cost is a fair consideration at any point in treatment. If you're weighing up whether to continue privately, our page on Wegovy pricing in the UK explains what drives costs and what a legitimate private prescription actually includes. For anyone thinking about starting, or reviewing whether their current treatment is right for them, speaking to our prescribers is the natural next step, the consultation is free, and clinical review happens the same day.