Wegovy side effects: what most people experience, and what needs medical attention

The first weeks: what it actually feels like to start Wegovy

Picture this: it's a Sunday evening, you've just taken your first Wegovy injection, and by Tuesday morning you feel faintly queasy at the sight of your usual lunch. That pattern is familiar to a lot of people starting treatment. Semaglutide slows how quickly food leaves the stomach, which is part of how it reduces appetite, and also why the gut sometimes protests, especially at the beginning.

The symptoms that come up most often are nausea, loose stools or constipation (sometimes both at different points), bloating, indigestion, burping, and fatigue. Headache and dizziness feature too, particularly if eating or drinking less than usual. Injection-site redness or itching can appear where the pen was used; rotating between the abdomen, thigh, and upper arm helps keep this manageable.

The NHS patient information for semaglutide describes these effects as common and notes they are typically at their worst just after starting or stepping up to a higher dose, then gradually improve. Eating smaller meals, going slowly with protein and fibre rather than heavy carbohydrates, and drinking plenty of water through the day all make a practical difference. If symptoms are genuinely difficult, your prescriber may suggest holding the current dose for longer before increasing, that conversation is worth having rather than stopping treatment silently.

A quick habit worth building: before each new pen, check the liquid in the cartridge. It should be clear and colourless. If it looks cloudy, discoloured, or contains particles, do not inject it and contact your pharmacy. Takes less than thirty seconds.

Less common side effects worth knowing about

Beyond the GI cluster, a smaller proportion of people on Wegovy experience effects that are less common but worth being aware of. Heart rate can increase slightly; if you notice your heart beating noticeably faster at rest, mention it at your next review. Gallstones are a recognised risk with significant weight loss generally, and GLP-1 medicines may contribute; symptoms include sharp pain in the upper right abdomen, sometimes spreading to the shoulder. Acute pancreatitis is rare but serious enough that the MHRA's Drug Safety Update in January 2026 specifically highlighted it for GLP-1 medicines as a class.

For people with a history of diabetic retinopathy, rapid changes in blood sugar regulation may affect vision; this is more relevant if you also use insulin or other diabetes medicines, and your prescriber will factor it in during assessment.

Hair thinning sometimes occurs a few months into treatment. This is usually related to the calorie deficit and rapid weight change rather than semaglutide itself, and tends to resolve. It's worth raising at a review rather than assuming it will pass, so it can be tracked properly. Our full Wegovy side-effects resource covers these less common effects in more depth.

When to get medical help without delay

Most side effects don't require urgent action. But some do, and it's important to know the difference before you're in the situation.

Seek emergency medical help (call 999 or go to A&E) if you experience severe stomach pain that doesn't ease, particularly if it reaches around to your back and is accompanied by vomiting. That pattern can indicate acute pancreatitis. Similarly, signs of a serious allergic reaction (swelling of the face, lips or throat, difficulty breathing, rapid heartbeat) need emergency attention.

Contact your GP or prescriber the same day if you notice symptoms of gallstones (sharp upper-right abdominal pain), significant changes to your vision, severe dehydration from repeated vomiting or diarrhoea, or any thoughts of self-harm or low mood that feel out of character. The NHS semaglutide page lists the full warning signs alongside their urgency level, and is worth saving to your phone.

You can also report any suspected side effect directly to the MHRA through the Yellow Card scheme, patients as well as clinicians can submit reports, and it genuinely informs post-market safety monitoring for newer medicines like Wegovy. For additional context on how serious effects are graded, the page on Wegovy's more serious side effects explains what the data shows at each severity level.

How a prescriber helps you manage side effects over time

Side effects rarely arrive all at once and then disappear for good. They shift with dose increases, with changes in what you eat, and with how your body adapts over months. That's why clinical oversight matters throughout treatment, not just at the start.

At nume, a GPhC-registered prescriber personally reviews every consultation and every repeat, not a form, not an algorithm, a real clinician reading your responses. Before each prescription is issued, your prescriber considers your current symptoms, how you've tolerated the most recent dose, and whether the next step is appropriate. If something's not working well, the answer might be staying at the current dose longer, adjusting when you inject, or reconsidering whether this medicine is the right fit. The Wegovy treatment overview explains how the dose schedule works in that broader context.

If you're weighing Wegovy against other options, the treatment comparison page sets out what's licensed in the UK and how the medicines differ. And if you have specific questions before committing, our team is reachable seven days a week. Side effect discussions are part of the free consultation, and if you'd like to read more before speaking to anyone, our pages covering what side effects Wegovy can cause, which of those side effects are considered the main ones to know about, and how common the most frequently reported side effects actually are give a thorough picture before you commit; our prescribers answer these questions regularly and don't expect you to have them figured out in advance.

Start your free consultation to talk through your situation with a prescriber and understand what to expect from treatment.