When Do Wegovy Side Effects Start — and How Long Do They Last?

The decision most people face: is what I'm feeling normal, and will it pass?

Starting Wegovy means committing to a titration schedule, and the question our prescribers hear most often is a simple one: is this nausea going to be my life now? The honest answer is that for the vast majority it is not. Side effects tend to cluster around two moments (the very first injection and each subsequent dose step) and then fade.

The starting dose (0.25mg weekly) is specifically designed to let your body adjust before the therapeutic doses begin. Nausea, queasiness, and a reduced appetite often arrive within the first two or three days of that first pen. By days seven to ten, many people find things have settled considerably. The pattern then repeats, usually more briefly, each time the dose increases. You can read more about the full side-effect picture on our Wegovy side effects overview.

Understanding this rhythm is itself useful. Knowing that the discomfort is most likely to peak in the first week, and that it is tied to the dose step rather than to the medicine in general, helps you distinguish normal adjustment from something that needs attention.

What the first few weeks typically feel like, and why

Semaglutide slows the rate at which the stomach empties and signals the brain that you are full sooner. Those same mechanisms that reduce appetite also explain why nausea, bloating, burping, and loose stools are the most reported effects, particularly early on. Constipation is common too, especially once nausea settles and eating volumes drop.

According to the NHS semaglutide medicines page, common side effects include nausea, vomiting, diarrhoea, constipation, stomach pain, fatigue, headache, dizziness, and injection-site reactions. Most are mild to moderate and self-limiting. Eating smaller meals, staying hydrated, and avoiding fatty or heavily spiced foods during the adjustment period makes a real difference for many people.

One practical note: keeping your pen in the fridge door means you see it every day and are less likely to miss a dose, but always let it come to room temperature before injecting, cold semaglutide can sting. For exact storage windows, check the Patient Information Leaflet that comes with your medication; the NHS and the medicine's SmPC on the electronic Medicines Compendium have the definitive guidance.

If you are curious about how side effect timing compares across semaglutide formulations, our page on when semaglutide side effects start covers the broader picture.

When to get medical help, the symptoms that change the calculation

Most side effects do not require urgent care, but some do. In January 2026, the MHRA issued a Drug Safety Update identifying acute pancreatitis as an infrequent but serious risk with GLP-1 receptor agonist medicines. The warning sign is severe and persistent stomach pain that spreads to the back, with or without vomiting. If that happens, stop eating and drinking and seek same-day medical attention, do not wait to see if it passes.

Other symptoms that warrant prompt contact with a doctor or 111 include: signs of a serious allergic reaction (swelling of the face, lips or throat, difficulty breathing), significant dehydration from repeated vomiting or diarrhoea, gallbladder-type pain (sharp pain in the upper right abdomen), and any sudden changes in vision. Low mood or thoughts of self-harm should also prompt immediate contact with a healthcare professional.

For anything you suspect is a side effect (even one you are unsure about) the MHRA Yellow Card scheme lets you report it directly. Patient reports genuinely shape how regulators monitor medicines after approval. Our guide to possible Wegovy side effects goes into more detail on the full list.

How to use this knowledge when deciding whether to start or continue

Side effects do not affect everyone equally. Some people sail through the first weeks; others find the first dose step rough. Age, diet, existing gut conditions, and how strictly the titration schedule is followed all play a role. No content page can tell you whether Wegovy is the right choice for your circumstances, that genuinely requires a clinical conversation.

What this page can do is help you arrive at that conversation better informed. If you have already started and are unsure whether what you are experiencing is within the expected range, our more detailed look at when Wegovy side effects start and our guide to what happens when you stop may both be worth reading first. Our Wegovy treatment page sets out the full picture of how treatment works in practice.

At nume, our prescribers discuss both suitability and the side-effect timeline during every consultation, it is a central part of the assessment, not an afterthought. If you would like to explore whether Wegovy is right for you, start your free consultation and a GPhC-registered prescriber will review your case the same day.