Side effects of Wegovy: what most people experience, and what needs urgent attention

The first few weeks: what's happening in your body and why it feels like this

Imagine you've just taken your first Wegovy pen. By day two or three, food that normally sounds appealing suddenly doesn't. You might feel queasy after a small meal, notice burping you weren't expecting, or find your stomach is unsettled in the morning. This is the GLP-1 effect in action: if you want to understand exactly how it works, our semaglutide page explains the medicine in full, including how it slows gastric emptying and signals to the brain that you're full sooner. Those same mechanisms are what drives the weight loss, but the gut takes a little time to adjust.

The most frequently reported effects people notice on Wegovy include nausea, vomiting, diarrhoea, constipation, indigestion and reflux, stomach discomfort and excessive burping. Fatigue and headache appear too, particularly in the first week or two of a dose. None of this is comfortable. Most people find the symptoms are manageable and ease significantly within a fortnight, especially if they eat smaller portions, avoid greasy food and stay well hydrated.

The NHS medicines information for semaglutide confirms that these gastrointestinal effects are common and outlines practical steps: eat slowly, keep meals small, avoid rich or spicy food during the adjustment period, and sip water regularly. The dose-escalation schedule exists partly for this reason, moving up gradually gives your system time to adapt before the next increase.

Injection-site reactions (redness, mild bruising, a small lump at the site) are also possible. Rotating sites between your abdomen, thigh and upper arm reduces this. Dizziness can occur, particularly if you stand up quickly after eating less than usual.

Side effects that are less common but worth knowing about

Beyond the GI picture, a smaller number of people on semaglutide report effects worth understanding before they start, including hair thinning, mood changes and sleep disruption, the current understanding is that hair thinning relates to the calorie restriction and physical change rather than the medicine itself, and it generally resolves. These are worth mentioning to your prescriber at your next review.

Gallbladder problems are an uncommon but documented risk. Rapid weight loss of any kind increases gallstone risk, and semaglutide is no exception. Symptoms to watch for include pain in the upper right abdomen, sometimes spreading to the shoulder, with nausea. If this persists or is severe, it needs medical assessment promptly.

For a broader look at the semaglutide side effects people commonly encounter, that page covers the mechanisms in more detail. And if you are weighing up whether Wegovy is the right fit for you at all, our treatment overview sets out what each option involves.

There is also a small risk of changes in heart rate and, in people with a history of diabetic eye disease, worsening of that condition, both are reasons why the prescriber's assessment before starting matters. Women using oral contraceptives should be aware that absorption of the pill may be less predictable if they are also on tirzepatide (a separate medicine); current evidence does not show the same concern with semaglutide, though your prescriber is the right person to confirm this for your situation.

When to get medical help urgently

Most Wegovy side effects sit in the manageable-but-unpleasant category. A smaller set of symptoms should prompt you to stop and seek help straight away.

Acute pancreatitis is a known but infrequent risk with GLP-1 medicines. In January 2026, the MHRA issued a Drug Safety Update highlighting pancreatitis across this class of treatment. The warning sign is severe, persistent pain in the stomach area that may radiate through to the back, sometimes with vomiting, sometimes without. If you experience this, do not wait to see if it passes. Get medical attention the same day.

Other urgent signs include: a serious allergic reaction (swelling of the face, lips or throat, difficulty breathing, rapid heartbeat); signs of severe dehydration from prolonged vomiting or diarrhoea (very dark urine, dizziness on standing, no urine output); and, in people with diabetes, symptoms of very low blood sugar if also on insulin or certain other medicines.

The less-discussed risks of Wegovy are covered in more depth for anyone who wants a fuller safety picture before starting, and our page on the bad effects of semaglutide is worth reading alongside it if you want to go into your first injection feeling fully informed. You can also report any suspected side effect (or a product you think might be counterfeit) to the MHRA using the Yellow Card reporting scheme. It takes five minutes and genuinely contributes to national safety monitoring.

Managing side effects: practical steps and when to ask your prescriber

The practical toolkit for getting through the early weeks is straightforward. Smaller meals, more slowly eaten. Cutting back on alcohol and fatty food during dose transitions. Keeping a water bottle nearby. If nausea hits in the morning, a light dry snack before getting out of bed can help. None of this is glamorous advice, but it works for most people.

If side effects are severe enough that you are unable to eat or drink, or if they have not improved after two weeks on a stable dose, tell your prescriber. They can advise on whether to stay at the current dose longer before increasing, adjust the timing of your injection, or review whether something else is contributing. Pushing through severe GI symptoms without flagging them is not the right approach, that is precisely what the aftercare check-ins are for.

At nume, our clinical team reviews every consultation personally, and prescribers are available for aftercare questions seven days a week. If you are looking at Wegovy and want to understand whether it suits your situation before committing to anything, speak to our prescribers via a free consultation, there is no obligation, and the assessment is thorough.