What to expect after your first Wegovy injection

Day one: why you probably will not feel very different

The first injection often passes quietly. Semaglutide at 0.25mg activates GLP-1 receptors involved in appetite signalling and slows gastric emptying, but the initial dose is calibrated for tolerability, not dramatic effect. Some people feel a mild heaviness after eating that afternoon. Others feel nothing at all. Both are fine.

What this means practically: do not judge the medicine by day one. The dose will be reviewed and increased by your prescriber roughly every four weeks, working up through the titration schedule. That graduated approach is intentional. It gives your gut time to adapt so that when you reach a maintenance dose, the adjustment has already happened gradually.

If you are curious about the full clinical picture of what changes across the programme, the overview of what happens over the course of Wegovy treatment covers the longer arc, from first pen through to maintenance.

Days two to seven: the signals worth paying attention to

By the second or third day, the effects of the injection become more noticeable for many people. Nausea is the most commonly reported one, it tends to arrive after eating rather than at rest, and it often improves if you eat smaller portions, avoid rich or fatty meals, and slow down while eating. Diarrhoea, constipation, indigestion and burping also feature in the side-effect profile described by the NHS medicines guidance on semaglutide.

One practical check you can do in under a minute: before your next dose, look at how much you ate at your last two or three meals compared with your usual portions. If the amounts are noticeably smaller without much effort, the medicine is working on appetite even before the scales move. That shift in hunger cues is often the earliest real signal that things are progressing.

Fatigue and mild headaches are also common in the first week, particularly if you are eating less and staying well-hydrated matters more than usual. Drink water consistently across the day rather than in large volumes at once.

For a detailed account of what to expect after your first Wegovy injection, including how symptoms typically shift across those opening seven days, the guide goes through the timeline in more detail.

When to seek medical help, not just reassurance

Mild nausea is expected. Severe, persistent abdominal pain that reaches the back is not, and requires prompt medical attention, it can be a sign of pancreatitis, which the MHRA highlighted in a January 2026 Drug Safety Update as a known, if infrequent, serious side effect of GLP-1 medicines. The same applies to signs of a significant allergic reaction, such as swelling, difficulty breathing, or a spreading rash.

Severe or prolonged vomiting and diarrhoea can cause dehydration, which puts strain on the kidneys. If you cannot keep fluids down for more than a day, contact your GP or NHS 111. Gallbladder-related pain (typically intense pain in the upper right abdomen) is also worth getting checked quickly rather than waiting it out.

You can report any suspected side effect from Wegovy through the MHRA Yellow Card scheme, which exists precisely to build a fuller picture of how medicines perform in the real world. Our aftercare team is also available seven days a week if you want a clinical steer before deciding whether to contact your GP.

Pen storage and what to do before your next dose

After injecting, store your remaining pens in the fridge. Wegovy must be kept at 2–8°C between doses. If a pen has been left out of the fridge, the rules on whether it is still usable depend on how long it was out and at what temperature, always check the Patient Information Leaflet for the exact figures rather than relying on memory or online estimates. Our page on how to store Wegovy after first use sets out the practical steps clearly.

Used pens are sharps and must be disposed of safely. A sealed sharps bin keeps things safe for everyone in the household. If you need one, a 1-litre sharps container is available alongside your treatment.

If you are weighing up whether Wegovy is right for you or want to understand the cost of private treatment before committing, the Wegovy pricing guide explains what a legitimate private prescription typically includes and what to watch for. Treatment is a prescription-only medicine; suitability is confirmed through a clinical consultation, not assumed. It is also worth reading about what happens after you stop taking Wegovy, so you can go into treatment with a clear picture of the longer-term picture. Our guide to the first injection of Wegovy walks you through exactly what to do on the day, from preparing your pen to choosing an injection site, if you want to feel confident before you start. When you are ready, you can check your eligibility with our prescribers at no cost.