Wegovy drug side effects: what to expect, what to watch for

The side effects most people actually notice on Wegovy

The dominant side effect category is gastrointestinal. In the STEP 1 trial (the main phase 3 study of semaglutide 2.4mg that underpinned Wegovy's UK licence) the most frequently reported reactions were nausea, diarrhoea, vomiting and constipation, with nausea affecting a substantial proportion of participants, particularly early in treatment. You can read a plain summary on the NHS semaglutide medicines page, which also lists less common effects including indigestion, reflux, burping, headache, dizziness and fatigue.

The graduated dose schedule exists partly for this reason. Starting at 0.25mg and stepping up roughly every four weeks gives your gut time to adjust before the dose climbs, and if you want to know what to expect at the very beginning, our page covering Wegovy .5 side effects explains what commonly arises at that first active dose. Side effects are typically worst in the 24–72 hours after an injection and ease as the week goes on. Eating smaller portions, avoiding fatty or very rich food, and staying well hydrated each makes a practical difference for many people during those early weeks.

Injection-site reactions (redness, itching or a small lump at the site) are also reported, though generally mild. Rotating between the abdomen, thigh and upper arm from week to week reduces the chance of localised irritation. If you are uncertain whether a symptom is expected, our frequently asked questions cover a number of the queries prescribers hear most often.

One quick habit worth building: before each weekly injection, scan how you have felt over the previous seven days and note anything unusual. It takes under a minute and gives you useful information to share with your prescriber at any review.

The side effects that need medical attention, and when to act fast

Most Wegovy side effects are an inconvenience rather than a danger. A handful are not, and it is worth being clear on the difference before you start.

Acute pancreatitis is the most significant. In January 2026 the MHRA updated prescribers about GLP-1 receptor agonists and pancreatitis, confirming it as an infrequent but serious risk. The symptom pattern to recognise is severe, persistent abdominal pain that may spread towards the back, sometimes alongside vomiting. If that happens, stop eating and drinking and get medical help promptly, do not wait to see if it passes. The MHRA's Yellow Card reporting tool is where you or your prescriber can log any serious suspected reaction.

Other signals worth acting on include: signs of a severe allergic reaction (swelling of the face, lips or throat; difficulty breathing; rapid heartbeat); symptoms of gallbladder problems such as upper-right abdominal pain, fever or jaundice; and significant dehydration if severe vomiting or diarrhoea has stopped you keeping fluids down. Kidney function can deteriorate when the body is very dehydrated, so persistent inability to drink is a reason to seek same-day medical advice rather than manage at home.

People with a history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2 should not use semaglutide; that assessment happens at the prescribing stage. If you notice any unusual neck lump or persistent hoarseness, mention it to a clinician. A fuller picture of Wegovy's recognised side effects (including very rare events) is in our detailed guide to Wegovy side effects.

When side effects don't appear (and why that's fine

A recurring question our prescribers field is some version of: "I haven't felt anything) am I getting a real pen?" It is a fair question given how prominently nausea features in discussions of GLP-1 medicines. The answer is straightforward: side effect experience varies considerably between individuals, and the absence of prominent GI symptoms is not a sign that the medicine isn't working.

Genetics, gut sensitivity, baseline diet and individual receptor response all play a role. Some people complete the full titration schedule with nothing more than occasional mild bloating. Others find the first few weeks genuinely uncomfortable, and our guide to side effects from Wegovy covers the full range of what people report across the treatment period. Neither pattern predicts weight outcomes, and neither is wrong. If you are in the first group, our page on experiencing no side effects on Wegovy explores this in more detail.

What does matter is that any pen you use comes from a verified, regulated supply chain. Counterfeit semaglutide pens (which have been seized in significant quantities by the MHRA) carry unpredictable risks precisely because their contents are unknown. The safe route is a prescription from a registered prescriber, dispensed by a GPhC-registered pharmacy you can verify by name and number.

Side effects as part of the treatment decision, not a reason to avoid asking

Whether Wegovy is the right choice for you involves weighing a documented side effect profile against the health risks that excess weight carries for your particular circumstances. That is a clinical conversation, not something to resolve by reading a list. NICE's recommendation of semaglutide for weight management, set out in TA875, reflects a considered view that the benefits outweigh risks for appropriately assessed patients.

At nume, our prescribers walk through your health history, current medicines and relevant risk factors before anything is prescribed, and they remain available to you afterwards through priority aftercare seven days a week. If a side effect appears mid-treatment and you are unsure whether it warrants action, a useful starting point is understanding how long Wegovy side effects last, which our dedicated page explains in detail. Our clinical team's background is on the site if you would like to know more about who reviews your case.

If you are still weighing up Wegovy against other licensed options, our weight-loss treatment overview sets out the full picture. And if you have questions about cost alongside this clinical decision, the Wegovy pricing page covers what private treatment typically involves. When you are ready to have side effects and suitability assessed properly, start your free consultation and our prescribers will take it from there.