Your first week on Wegovy: what actually happens

You've just done your first injection, here is what the next seven days often look like

You've pressed the pen against your thigh or abdomen, heard the click, and now you're wondering what's supposed to happen. For most people: not very much, not yet. The 0.25 mg dose is calibrated to ease your system into treatment rather than hit it hard. A small number of people feel almost nothing different in week one. Others notice nausea within a few hours of the first injection, usually mild and brief, sometimes arriving the day after rather than immediately. If you want a detailed walkthrough of what to expect as each day unfolds, our guide to Wegovy week 1 covers the timeline in full.

Gastrointestinal reactions are the most commonly reported effects at the start. Nausea tops the list, followed by loose stools, constipation (the two can alternate in the same person), indigestion and burping. These are well-documented in clinical data and described on the NHS's semaglutide medicines page. The reassuring pattern is that symptoms tied to a new dose tend to peak around day two or three and ease off as the week continues. Eating smaller meals, avoiding rich or fatty food, and staying well hydrated all help. Timing your injection for an evening or weekend when you can rest if needed is a practical adjustment many people find useful.

Fatigue and mild headache can also appear in the first week. These are not dangerous, they reflect the body adjusting to slower gastric emptying and, possibly, a subtle shift in calorie intake. If symptoms feel genuinely severe or you vomit repeatedly and cannot keep fluids down, contact your prescriber or the aftercare team. That is not the expected experience, and it is worth flagging early.

Will you feel less hungry in the first week?

Some people notice it almost immediately. Meals feel satisfying with less on the plate. The urge to snack in the evening quietens a little. Others feel no appetite change in week one at all, and that is equally normal. Semaglutide's effect on hunger builds gradually as the drug reaches a steady concentration; at 0.25 mg you are at the floor of the therapeutic range, so dramatic appetite suppression this early is not guaranteed and not the goal.

What you are more likely to notice is a small shift in how quickly you feel full rather than a wholesale loss of interest in food. Pay attention to that signal, it is the mechanism working as it should. Eating slowly and stopping when you are comfortably full (rather than when the plate is empty) will serve you well throughout treatment, not just this week. How long Wegovy takes to work meaningfully is a longer conversation, but the foundations are laid in these early weeks.

One thing our clinical team hears regularly: people worry that because they don't feel much in week one, the treatment isn't working for them. That worry is understandable, and it almost always turns out to be unfounded. The dose escalation schedule exists precisely because the medicine needs time, and your body needs time alongside it.

What week one does not tell you about your results

The STEP 1 trial, which established the evidence base for Wegovy 2.4 mg, ran for 68 weeks and found an average body weight reduction of around 15% at the maintenance dose, as published in the New England Journal of Medicine. Week one contributes almost nothing to that figure on its own. The weight-loss trajectory is strongly back-weighted: results accumulate through the titration phase and beyond as the dose rises and appetite suppression deepens.

Some people do see a small movement on the scales in the first fortnight, partly water, partly a mild calorie reduction from eating a little less. Do not read too much into it either way. A week one without visible scale movement is not a sign of failure; a small early drop does not predict your eventual outcome. Both are within the normal range. What to expect after a full month on Wegovy gives a more useful early benchmark than the first week alone.

It is also worth knowing that how your first week feels does not reliably predict long-term tolerability. People who feel quite nauseous in week one often find the next few weeks considerably easier, as the body adapts. The gradual dose steps (0.25 mg, then 0.5 mg, then 1.0 mg and so on) are designed to make that adaptation as smooth as possible. You can read about what shifts as the weeks progress on the week two page and, for a fuller picture of the early months, week four is when many people start to feel a more settled pattern. There is genuinely no rush.

If you are still deciding whether to start, or want to understand more about your eligibility, checking your eligibility with our prescribers costs nothing and carries no obligation.