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Start journey Learn moreHow Wegovy's side effects actually behave, from first pen to long-term use
What the STEP 1 trial recorded happening to people
Start with the evidence, because it sets realistic expectations. In the STEP 1 study, published in the New England Journal of Medicine, adults taking semaglutide 2.4mg over 68 weeks lost around 15% of their body weight on average alongside diet and activity changes. The side effects reported alongside that result were overwhelmingly gastrointestinal.
Nausea led the list, followed by diarrhoea, vomiting and constipation. Most people who experienced these described them as mild or moderate, and they clustered around the points where the dose went up. That pattern matters: the profile you read about in a trial is not a permanent state, it is largely a settling-in phase.
The NHS medicines guide to semaglutide lists the same everyday effects and describes them as common rather than rare. Reading the trial and the NHS page together gives you the honest version: side effects are likely at some point, unpleasant symptoms are usually short-lived, and a smaller group sails through with very little. If you want the reassuring end of that range, some people report barely any side effects on Wegovy, though that isn't something anyone can promise you in advance.
Why the low starting dose exists at all
Wegovy is never begun at its full strength. Treatment opens at 0.25mg weekly, and a prescriber steps it up roughly every four weeks through 0.5mg, 1.0mg and 1.7mg toward the maintenance dose. That first dose isn't doing much for weight; its job is to let your gut adjust before the stronger doses arrive.
This is exactly why the sharpest symptoms tend to appear in the first week and again after each step up. Slowing gastric emptying is part of how semaglutide curbs appetite, and your digestive system needs time to adapt to that. Rush the schedule and nausea gets worse; give it room and most people find each new dose is easier the second and third week in.
People often ask what to expect on the very first day of Wegovy versus day two, when a slow build of queasiness can catch you off guard. If side effects feel heavier than you can manage at a given dose, that is a prescriber conversation, not a reason to change things yourself. Dose timing and any adjustment always sit with the clinician and the Patient Information Leaflet, never with a page like this one.
The digestive symptoms most people notice
Nausea is the headline, but the fuller list on Wegovy is worth knowing so nothing takes you by surprise. Reflux and indigestion are common, and so is trapped wind. Plenty of people are startled by the burping in particular, sometimes with a sulphurous edge, which is why we cover why Wegovy burps can taste like eggs separately.
Bowel habits swing both ways. Some people get diarrhoea on Wegovy, others the opposite with constipation, and a few alternate between the two. Heartburn shows up for some, tiredness for others, and headaches feature on the NHS common list too.
The practical points help. Smaller meals, easing off very fatty or rich food, staying hydrated and giving your body a chance after each dose increase all take the edge off the digestive effects. Fatigue is real for a portion of people, especially early on, and we look at whether Wegovy makes you tired in its own right. None of this is a sign the medicine is wrong for you; it is usually your system recalibrating. If a symptom is severe, doesn't settle, or worries you, that's the moment to check in rather than push through quietly.
The less common effects, including the eye and mood ones
Beyond the digestive stuff, a handful of less frequent effects deserve a clear mention rather than a footnote. Some people report hair thinning during rapid weight loss; this is usually linked to the weight change itself rather than the drug directly, and we explain the pattern behind Wegovy and hair loss.
Gallbladder problems can occur, more so when weight comes off quickly. There is also a diabetic retinopathy signal in people with diabetes, which is why any changes to your vision on Wegovy should be flagged to a clinician promptly. Low mood and, rarely, thoughts of self-harm have been noted with weight-loss medicines generally, and those are always worth raising early.
Dehydration is the quiet risk that ties several of these together. If vomiting or diarrhoea is heavy, fluid loss can strain the kidneys, so keeping fluids up during a bad spell isn't optional. The MHRA also advises using contraception on semaglutide and allowing a wash-out before trying to conceive; Wegovy isn't recommended in pregnancy, while breastfeeding or if you're trying to get pregnant, and it isn't licensed for under-18s. If you're curious how the broader picture compares across the molecule, our page on semaglutide side effects takes the wider view.
When to get medical help urgently
Most side effects are manageable at home. A few are not, and knowing the difference matters more than anything else on this page. Get urgent medical help for severe, persistent stomach pain that may spread through to your back, with or without vomiting.
That warning comes straight from the MHRA's Drug Safety Update of 29 January 2026, which highlighted acute pancreatitis as an uncommon but potentially serious side effect of GLP-1 medicines. It is rare, but it needs same-day attention, not a wait-and-see. You can read the regulator's advice on the MHRA Drug Safety Update pages.
Other signs that warrant prompt medical contact: symptoms of a gallbladder problem such as sudden upper-abdominal pain, signs of dehydration after heavy sickness or diarrhoea, a severe allergic reaction, sudden changes to your vision, or any thoughts of harming yourself. None of these are common, and listing them isn't meant to frighten you off a medicine the MHRA has assessed and licensed. It's simply the responsible version of the facts. If you're weighing up the risk side honestly, our discussion of whether Wegovy is safe and the most serious potential side effects both go deeper without the alarmism.
How long side effects tend to stick around
The honest answer is that most digestive side effects are a phase, not a fixture. For a lot of people, the worst of the nausea and the wind fades within days to a couple of weeks of starting or stepping up, once the body adapts to the slower gastric emptying.
That said, timelines vary genuinely from person to person, and a minority find symptoms linger longer or return with each dose increase. We've pulled the patterns together in detail on how long Wegovy side effects last, because it's one of the questions our prescribers hear most weeks. The general shape holds: sharp at the transitions, calmer in between.
Long-term, the picture is more reassuring than many people expect, though it is still monitored. Semaglutide (Wegovy) carries the MHRA Black Triangle symbol, meaning it's under additional safety surveillance, which is precisely how emerging signals get caught. If you're thinking years rather than weeks, our page on long-term Wegovy side effects covers what's known and what's still being studied. Ongoing effects are always worth a prescriber review rather than tolerating in silence, because sometimes a small adjustment makes a real difference.
Reporting side effects, and how our consultation handles them
If you experience a suspected side effect on Wegovy, you can report it directly through the MHRA's Yellow Card scheme. It takes a few minutes, it's open to patients as well as clinicians, and every report feeds the UK's real-world safety monitoring. It's a genuinely useful thing to do, not box-ticking.
On our side, side effects aren't an afterthought bolted onto a sale. When you start a free consultation, a named GPhC-registered prescriber reads your answers the same day, checks your history, and talks through what you might feel and how to manage it before anything is approved. There's no algorithm signing off in the background. Aftercare runs seven days a week, so if something crops up once you've started, there's someone to ask rather than a leaflet to squint at.
Practically, once a prescriber approves treatment it's dispatched the same day if you've ordered before 12pm on a weekday, and it arrives free the next working day by DPD in a plain, unbranded box you can track on your phone. The pen is inside, ready to store in the fridge. That's the whole point of doing this through a regulated pharmacy: real oversight, not just a parcel. Our prescribers discuss suitability and side effects with you as part of the consultation, so speak to our prescribers before you start.
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