What to expect in week 1 on Wegovy

The 0.25 mg dose: what it is actually doing in your body

The decision most people face in week 1 is whether what they are experiencing is normal. The short answer is: almost certainly yes, even if that experience is "nothing much at all."

Semaglutide, the active ingredient in Wegovy, attaches to GLP-1 receptors involved in appetite signalling and the rate at which your stomach empties. At 0.25 mg, the dose is low enough that the body's response is often subtle. Some people notice food feels less appealing by day three or four, or that they stop halfway through a meal without particularly trying. Others get through the whole first week without any obvious signal that the medicine is doing anything. Both are within the normal range.

What the starting dose is not meant to do is produce the kind of appetite suppression seen at 1.7 mg or 2.4 mg. Think of it as a calibration period: the pen in the fridge door is there for weeks, not one injection. The full timeline for Wegovy to take effect typically runs to several months at maintenance dose, and week 1 is the first small step on that path. The NHS's patient-level guidance on semaglutide explains the dose escalation schedule and what to expect at each stage.

If you have already had your consultation and are partway through your first week, this is also a good moment to re-read the Patient Information Leaflet supplied with your pen, it covers what the starting dose is designed to do and when to contact your prescriber.

Side effects in week 1: what is common, what passes, what to act on

Nausea is the side effect people most frequently ask about in the second week, and it often starts in week one. Alongside nausea, some people notice constipation, loose stools, bloating, or a general feeling of fullness that sits uncomfortably. These effects are not random: they reflect semaglutide slowing gastric emptying, which is part of how it reduces appetite, but which the gut takes time to accommodate.

For most people these effects are mild to moderate and settle within the first two weeks without any change to the dose. Eating smaller portions, avoiding high-fat meals, staying hydrated and giving yourself time after eating before lying down all tend to help. Your prescriber and the Patient Information Leaflet are the right source of advice if symptoms are more than mild.

A small number of people experience something more acute. Severe or persistent stomach pain that spreads to the back (with or without vomiting) should be assessed by a doctor promptly, as it may indicate pancreatitis. The MHRA flagged acute pancreatitis as a known, infrequent but serious risk with GLP-1 medicines in a Drug Safety Update published in January 2026. This is not a reason to avoid treatment, but it is a reason to know the symptom and act on it quickly if it occurs.

Signs of an allergic reaction (swelling, difficulty breathing, a widespread rash) also require urgent medical attention. These are rare. Week 1 is an opportunity to note your body's response carefully, not to worry about every sensation, but to be alert to anything severe or persistent.

Weight loss in week 1: what the evidence actually says

People search for Wegovy week 1 results expecting a number, and the honest answer is that the number is usually small. The STEP 1 trial, published in the New England Journal of Medicine, reported an average body-weight reduction of around 15% over 68 weeks at the 2.4 mg maintenance dose. The vast majority of that reduction accumulated over months, not days. At 0.25 mg for four weeks, weight change on the scale in week 1 often reflects fluid shifts, bowel habits and daily variation more than any pharmacological effect.

That does not mean nothing is happening. The mechanism is active from the first dose. But if you weigh yourself on day seven and the number has barely moved, that is consistent with clinical evidence, not a sign the medicine is not working for you. A more informative comparison point is how things look at the end of the first month, once the initial dose has been in place long enough to show a trend. For a fuller sense of the typical pattern, the Wegovy treatment overview sets out what the research shows across the full titration schedule.

Separately, weight loss in week 1 specifically varies considerably between individuals, body composition, starting weight, dietary habits and how much appetite suppression the dose produces all play a part. A modest or negligible first-week reading is not a predictor of long-term outcome.

Getting started through a regulated UK pathway

Wegovy is a prescription-only medicine. The only legal route to it in the UK is a prescription following clinical assessment by a registered prescriber, there is no shortcut, and sellers offering it without that step should be avoided. The GPhC pharmacy register lets you verify any online pharmacy before you hand over personal or medical details.

If you are thinking about starting and want to understand whether you are likely to be eligible, you can read more on the weight-loss treatment overview. The cost of private treatment is a common question; the context around Wegovy pricing in the UK is worth reading before making a decision based on headline figures alone.

If you are ready to take the next step, check your eligibility with our prescribers, consultation is free, and every assessment is reviewed the same day by a GPhC-registered prescriber, not automated software.