Wegovy Nebenwirkungen: Side Effects Explained for UK Patients

You've just started Wegovy, and your stomach is telling you about it

That queasy feeling in the first few days is the experience most people describe first. Semaglutide slows the rate at which your stomach empties, which is part of how it reduces appetite, but it also explains why the gut reacts. Nausea is the most commonly reported effect in clinical trials: in the STEP 1 study, it occurred in around 44% of participants on semaglutide 2.4mg, compared with roughly 16% on placebo. For most people it's unpleasant rather than severe, and it tends to peak in the 24–48 hours after an injection, then gradually fade.

Alongside nausea, diarrhoea and constipation both appear in the data, sometimes alternating, which patients often find puzzling. Vomiting, indigestion, bloating and burping are also on the list. None of this is unusual for a medicine that works on gut-hormone receptors. The pattern tends to repeat, at a milder level, each time the dose steps up. Eating a little before the injection can help some people; smaller, lower-fat meals during the early weeks matter more than any single trick.

If you're managing this alongside a normal week (picking up children, heading to work) it helps to know that symptoms are usually worst the day after the injection rather than continuously. Planning the injection for a Thursday evening, for example, means the roughest hours fall over the weekend rather than a Monday morning. Small, practical choices like that make a real difference to tolerability. Our guide to starting Wegovy for the first time covers more on what those first weeks look like.

Side effects that need a call to your GP or prescriber, not just watchful waiting

Most Wegovy side effects are in the uncomfortable-but-manageable category. A smaller number need prompt medical attention. The most important is pancreatitis. In January 2026 the MHRA issued a Drug Safety Update specifically flagging acute pancreatitis as a known but infrequent risk with GLP-1 medicines: severe, persistent abdominal pain that radiates to the back, with or without vomiting, needs same-day medical assessment. This is not the ordinary bloating or nausea of the first week, it's a different quality of pain, and the distinction matters.

Gallbladder problems are also listed in the semaglutide safety data. Significant weight loss of any kind can increase gallstone risk, and Wegovy is no exception. Symptoms to watch for include upper-right abdominal pain, especially after eating, alongside fever or jaundice. Dehydration from persistent vomiting or diarrhoea can, in turn, strain the kidneys, staying hydrated isn't optional if GI effects are significant.

Less commonly, people report fatigue, headache and dizziness, particularly in the early stages. Injection-site reactions are possible wherever the pen is used. On very rare occasions, allergic reactions have been reported; swelling of the face or throat, difficulty breathing or a fast heartbeat warrant emergency help immediately. If you have questions about a symptom you're experiencing, our aftercare team is available seven days a week.

The January 2026 MHRA update and what it means for people on Wegovy

The MHRA's Drug Safety Update of 29 January 2026 drew attention to pancreatitis across GLP-1 receptor agonists as a class. It was not a signal that the medicines were becoming less safe, pancreatitis had always been listed in the semaglutide SmPC. The update reinforced that prescribers and patients should both know the symptom pattern and act on it quickly if it appears.

Wegovy carries a Black Triangle (▼) designation from the MHRA, meaning it is subject to additional monitoring because it is relatively new. This is routine for recently authorised medicines and does not indicate a higher danger level. What it does mean is that reporting suspected side effects matters more than usual: data collected through the Yellow Card scheme feeds directly into MHRA safety reviews. You can report as a patient, not just as a healthcare professional, at yellowcard.mhra.gov.uk.

For full prescribing detail, including the complete contraindications list and storage requirements, the authoritative reference is the Wegovy Summary of Product Characteristics, available via the electronic Medicines Compendium. The NHS semaglutide page gives a clear patient-facing summary of the same information. If you're weighing up the full picture of semaglutide's profile before deciding, our semaglutide overview covers the mechanism, evidence and licensed uses in one place.

Specific situations: contraception, pregnancy and other medicines

Because Wegovy slows gastric emptying, it can affect the absorption of other oral medicines taken at the same time. This is worth discussing with your prescriber if you take anything regularly by mouth. For oral contraceptives specifically, NHS guidance notes there is no equivalent evidence of reduced pill effectiveness for semaglutide to that seen with tirzepatide, but the topic should still be discussed at your consultation, because individual circumstances vary.

Wegovy is not recommended during pregnancy, breastfeeding, or if you are actively trying to conceive. The MHRA advises using effective contraception while on treatment. If your situation changes, contact your prescriber before your next dose. People under 18 are also outside the licensed indication, and the medicine should not be used in this group.

If you're considering whether Wegovy is right for you, or you're wondering how it compares with other licensed options, our weight-loss treatment overview sets out the landscape clearly. The newer 7.2mg Wegovy pen, approved by the MHRA in April 2026, extended the maximum maintenance dose; its side-effect profile is broadly consistent with lower doses, though GI effects at higher doses remain the most common reason people pause or slow titration. Suitability for any dose is always a clinical decision, a prescriber reviews the full picture, not just the BMI. If you have questions about how the Wegovy 0.5mg starting dose fits into the titration schedule, or want to understand what changes as you move through the steps, our pages on Wegovy and Wegovy dose two walk through each stage in detail. If you're ready to find out whether Wegovy is clinically appropriate for you, start your free consultation and a GPhC-registered prescriber will review your answers the same day.