Wegovy day by day: what actually happens after your first dose

Days 1–3: the injection is done, now what?

Picture this: your pen arrives in a plain, unbranded box with DPD tracking, you put it in the fridge door, and the following morning you do your first injection. The next 72 hours are often the most unpredictable of the whole treatment.

Most people feel fine on day one. The semaglutide is entering your system gradually; the peak plasma concentration for a subcutaneous dose comes days later, not hours. By day two some people start to notice a low-grade nausea, not dramatic, but there. Fatigue is common too, along with a mild headache in some cases. Others feel nothing out of the ordinary at all.

The NHS notes that nausea, vomiting, diarrhoea and constipation are the most frequently reported side effects with semaglutide, and they tend to cluster in the early days after an injection or a dose step. The NHS semaglutide medicines page has a full side-effect breakdown worth reading before you start. If you find the first couple of days manageable, the news is usually good: most people find these early effects settle within one to two weeks at a given dose. Eating smaller portions, staying well-hydrated, and avoiding high-fat or very rich food in the first day or two after injecting tends to help.

What you almost certainly won't feel yet is a meaningful shift in appetite. That takes longer, be patient with it at this stage.

Days 4–7: the middle of the week, and the first signs of appetite change

For many people, somewhere between day three and day five is when hunger starts to feel different. Not absent, but quieter. You reach for a snack and realise you're not actually hungry. You stop halfway through a meal without forcing it. This is the GLP-1 mechanism doing what it's designed to do: slowing gastric emptying and adjusting the hormonal signals that normally drive appetite.

The gastrointestinal symptoms, if you had them, often ease off around now. That said, constipation can linger longer than nausea, fibre and fluid intake matter more during treatment than most people expect.

By day six or seven you're approaching the next injection. Some people notice that hunger edges back slightly in the final day before their next dose; this is normal at the lower starting doses and usually lessens as the dose increases over subsequent months. The full clinical picture of how semaglutide works across the titration schedule explains why the early weeks feel different from month three or four.

If you're curious about how day one specifically tends to compare with day four in terms of side-effect timing, our Wegovy day one guide covers the first 24 hours in detail, and the day four page picks up from there.

Weeks 2–4: the pattern starts to settle

After the first injection, each subsequent week tends to be somewhat easier than the last at the same dose. The second injection often brings milder nausea than the first because your body has started to adjust to the medicine's presence. By the third and fourth week, many people describe the GI side effects as background noise rather than a disruption.

The appetite suppression, by contrast, often deepens. Portion sizes shrink without much conscious effort. The desire to graze between meals fades. This is also the window where the behavioural shift that supports the clinical results begins to take root, not just eating less, but starting to notice a different relationship with food.

The STEP 1 trial, published in the New England Journal of Medicine, followed people taking 2.4 mg semaglutide over 68 weeks and recorded an average body-weight reduction of around 15%. That figure is a population average across the full treatment course. What happens in week three is part of a much longer arc; it's not where the meaningful numbers land. Understanding the cost of Wegovy over that full course is worth doing at this stage too, before committing to the longer titration.

If your dose increases at the four-week mark (which your prescriber will decide based on how you've tolerated the starter dose) the early-days side-effect pattern can reset slightly. Think of a dose increase as a mini week one: the same caution with food, the same patience for a few days.

What to watch for, and when to act

Most of what people experience day by day with Wegovy is uncomfortable rather than dangerous. The side effects described above are expected and documented. There are a handful of things that warrant prompt medical attention, though, and it's worth knowing them before you start.

Severe, persistent stomach pain (particularly if it radiates toward your back and comes with vomiting) should be assessed urgently. The MHRA highlighted acute pancreatitis as a known, if infrequent, risk with GLP-1 medicines in a Drug Safety Update published in January 2026; this is the symptom profile to watch for. Gallbladder symptoms (sharp pain under the right ribs) are also worth flagging to your GP rather than waiting. If GI side effects are so severe that you can't keep fluids down, dehydration becomes a real concern, call your prescriber or 111.

Signs of an allergic reaction (swelling, difficulty breathing, widespread rash) require emergency care. And if you notice low mood or any thoughts of self-harm, tell your prescriber promptly, these are listed in the product information as things to monitor.

For anything short of the above, your prescriber and our aftercare team at nume support are there seven days a week. The day-by-day experience is something our clinical team, including our lead prescriber, see questions about regularly, there's rarely a concern that hasn't come up before. If you're still weighing up whether Wegovy is right for you, a free consultation with our prescribers is the logical next step.