Reported Side Effects of Wegovy: What Clinical Evidence and Real-World Data Tell Us

What the STEP 1 trial data actually reported

The clearest picture of Wegovy's side-effect profile comes from the STEP 1 phase 3 trial, published in the New England Journal of Medicine in 2021. Over 68 weeks, adults taking semaglutide 2.4 mg reported gastrointestinal effects far more often than those on placebo. Nausea was the most common, affecting around 44% of the semaglutide group compared with roughly 16% on placebo. Diarrhoea, vomiting, constipation and abdominal pain were also more frequent in the treatment arm.

Crucially, the trial found that the majority of these events were mild or moderate in severity. Discontinuation due to GI side effects occurred in about 4–5% of participants on semaglutide, suggesting that most people tolerated the medicine well enough to continue. The trial also captured less common effects: fatigue, headache, dizziness and injection-site reactions appeared at low rates, and were generally transient.

The NHS medicines page for semaglutide summarises these findings in accessible terms and lists which side effects to watch for, which to report to a pharmacist, and which require immediate medical help. It is a sensible first read before starting treatment.

Why side effects tend to cluster around dose increases

Semaglutide slows gastric emptying, a mechanism that underpins both its appetite-reducing effects and its GI side-effect profile. When the dose steps up, the stomach takes longer to empty than it did at the previous level, which is why nausea and discomfort often resurface briefly after each increase before settling again.

The titration schedule, which moves gradually from 0.25 mg through to the 2.4 mg maintenance dose over roughly four months, exists partly for this reason: each increment gives the body time to adjust. People who move through dose steps more slowly, under prescriber guidance, often find the side-effect burden easier to manage.

Practical strategies reported by trial participants include eating smaller portions, avoiding fatty or rich foods in the early weeks, staying well hydrated and not lying down immediately after eating. None of these replace clinical advice, and your prescriber is the right person to talk through what suits your situation. For a wider picture of how people describe living with these effects, the consumer experience reports we have gathered offer a useful complement to the clinical data.

It is also worth noting that bloating specifically is a question many people raise. Whether bloating is a side effect of Wegovy, and how common it is relative to other GI symptoms, is explored in its own section for anyone particularly concerned about that symptom.

When to get medical help: the side effects that cannot wait

Most of what people report with Wegovy is unpleasant rather than dangerous. A small number of effects, however, need prompt attention.

In January 2026 the MHRA issued a Drug Safety Update for GLP-1 receptor agonists, highlighting acute pancreatitis as an infrequent but potentially serious risk. The warning sign is severe, persistent abdominal pain that may radiate through to the back, with or without vomiting. If this occurs, stop treatment and seek urgent medical help rather than waiting to see whether it passes.

Other situations that warrant same-day contact with a healthcare professional include: signs of a serious allergic reaction (swelling of the face, lips or throat, difficulty breathing, rapid heartbeat); symptoms of gallbladder problems such as intense pain in the upper right abdomen; signs of dehydration if vomiting or diarrhoea has been severe; and any sudden changes in vision, which may be relevant for people with a history of diabetic retinopathy. A low mood or thoughts of self-harm should also prompt contact with your GP or mental health services promptly.

The Yellow Card scheme is the MHRA's national system for recording suspected side effects and allows patients to report directly, without going through a doctor first. Reports from real-world use shape ongoing safety monitoring for medicines like Wegovy, so they genuinely matter. If you have a query and are already a patient with us, our team is available through the aftercare support line seven days a week.

What the broader side-effect picture looks like for the people who stay on treatment

Beyond the GI effects, a smaller proportion of Wegovy users report hair thinning, particularly in the first few months. This is thought to be related to rapid calorie reduction rather than semaglutide itself, and it tends to resolve without intervention. Muscle loss is a related concern when weight comes off quickly, which is why maintaining adequate protein intake and continuing physical activity are consistently recommended alongside treatment.

The full side-effect profile, including frequency categories and contraindications, is set out in the Wegovy Summary of Product Characteristics, available through the electronic Medicines Compendium. For a structured overview of all reported effects from common through to rare, the complete side effects reference covers each category in detail.

For anyone considering treatment, knowing that these effects exist is not the same as knowing they will apply to you. Individual responses vary considerably, and if you want to understand what has been reported across the full dose range, our guide to Wegovy side effects sets out the clinical picture in one place. Our prescribers discuss this during every consultation, and no prescription is issued without a genuine clinical conversation about your health history, any medicines you currently take and how to minimise avoidable discomfort. If you would like to explore whether Wegovy is appropriate for you, the Wegovy treatment page sets out the full picture, and you can read about our wider weight-loss treatment options alongside it, including a closer look at what counts as a side effect of Wegovy and how each one is typically managed.