Wegovy risks and side effects: what actually happens, and when to act

Your first few weeks on Wegovy: what the gut is doing and why

Picture the scenario: your pen arrives, tracked to your door by DPD in a plain, unmarked box, and you're reading the Patient Information Leaflet before that first injection. The most common reactions listed there are gastrointestinal, nausea, vomiting, diarrhoea, constipation, indigestion, reflux, burping. That list can look alarming stacked up in one column.

What the leaflet cannot easily convey is that these symptoms follow a pattern. Semaglutide slows gastric emptying and acts on appetite centres in the brain, and your gut needs time to adjust. Nausea tends to be sharpest after starting treatment and again after each dose step, the 0.25mg, 0.5mg, 1.0mg, 1.7mg sequence is deliberately graduated for exactly this reason, titrated by your prescriber to give your system breathing room. For most people the discomfort softens within a week or two. Eating smaller portions, avoiding very fatty meals, and staying well-hydrated helps considerably; the NHS medicines page for semaglutide sets out practical advice on managing these effects day to day.

Headache, fatigue, and dizziness also appear in the clinical data, less discussed but worth knowing. Injection-site reactions (redness, itching, a small lump) occur in some people and usually resolve quickly with site rotation between abdomen, thigh, and upper arm. The full side-effect profile for Wegovy covers these in more depth if you want the granular picture.

Side effects that need prompt medical attention

There is a meaningful difference between uncomfortable and urgent. Most GI symptoms fall in the uncomfortable category. A few do not.

Pancreatitis (inflammation of the pancreas) is uncommon, but the MHRA issued a Drug Safety Update in January 2026 reinforcing that GLP-1 medicines including semaglutide carry this known risk. The warning sign is severe, persistent abdominal pain that reaches through to the back, sometimes with vomiting. This is a 999 situation, not a wait-and-see one. Stop the injection and seek emergency care.

Gallbladder problems (gallstones or inflammation) are more common in people losing weight quickly regardless of the method, and semaglutide trial data reflects this. Symptoms include sharp pain in the upper-right abdomen, particularly after eating. Again: prompt medical attention, not reassurance-searching online.

Allergic reactions are rare but possible: swelling of the face, throat, or tongue, difficulty breathing, a rapid heartbeat. Any of these mean calling 999 immediately.

For people with type 2 diabetes taking other glucose-lowering medicines alongside Wegovy, blood sugar can drop further than expected. Discuss this specifically with your prescriber. And if you notice sudden changes in vision, contact your doctor promptly, this is noted in the semaglutide prescribing information in the context of diabetic eye disease. The full list of contraindications and cautions is detailed in the Wegovy SmPC on the eMC, which is the definitive clinical reference for prescribers and patients.

Longer-term and less-discussed risks worth knowing

The STEP 1 trial followed participants for 68 weeks at 2.4mg (long enough to generate a meaningful safety dataset) and the overall profile was consistent with the GLP-1 class. That said, Wegovy carries a Black Triangle (▼) designation from the MHRA, meaning it is still subject to additional post-marketing surveillance. This is standard for newer medicines and reflects regulatory diligence, not unusual danger.

Muscle loss is a practical concern raised in the context of rapid weight reduction on any treatment. Clinical guidance emphasises adequate protein intake and resistance exercise alongside semaglutide, not because it's mandatory fine print, but because preserving muscle affects how your body functions as weight comes down. If you want a thorough grounding before starting, our page covering semaglutide risks and side effects walks through what the trial data and real-world experience tell us. Your prescriber and, where appropriate, a dietitian are the right people to shape that plan for you specifically.

The long-term risks of Wegovy and what the emerging data show is a topic our clinical team keeps close watch on. The treatment is relatively new at the weight-management dose, and pharmacovigilance continues.

One group for whom the risk-benefit balance shifts significantly: anyone with a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2. Semaglutide is contraindicated in these cases, it is one of the first questions a thorough prescriber should ask. Our dedicated page on semaglutide risks covers this contraindication alongside others in detail, which is useful reading before your consultation.

Who should not take Wegovy, and what to discuss before starting

Wegovy is not licensed for people under 18, and it is not recommended during pregnancy, while breastfeeding, or in the period when someone is actively trying to conceive. The MHRA advises using effective contraception while on treatment. For women taking the combined oral contraceptive pill, it is worth discussing with your prescriber whether absorption of the pill might be affected (particularly at higher dose steps) and whether an additional barrier method is sensible in the short term.

A history of pancreatitis, significant digestive conditions, or severe kidney or liver problems all warrant careful prescriber review before starting. These are not automatic barriers, but they are conversations that need to happen, and they are exactly the kind of thing a proper clinical consultation exists to surface. Anyone weighing up whether this treatment is suitable will find it helpful to read about the risks of taking Wegovy before their first appointment, so the conversation with the prescriber can be as informed as possible. At nume, a GPhC-registered Independent Prescriber reads every assessment personally on the day it arrives, a real clinician, not a decision algorithm. Our clinical team is there to work through these questions with you, and our prescribers discuss suitability and side effects as part of every consultation.

If you are already on Wegovy through another provider and want to understand how our review process works, the about us page covers our pharmacy's GPhC registration and clinical governance. Understanding the Wegovy risks that apply to your specific health profile is something our prescribers will take time to go through with you during that review. And if anything about your treatment worries you between consultations, our support team is available seven days a week. To explore whether Wegovy or another licensed treatment might be appropriate for you, the starting point is a free consultation with our prescribers.