Wegovy's safety profile: what the evidence actually shows

Step 1: what to expect when you first start

Wegovy is introduced at a low starting dose precisely because the body needs time to adjust to the way semaglutide slows gastric emptying and reduces appetite. The standard titration schedule climbs gradually over several months, and much of that structure exists to reduce the intensity of side effects rather than for any pharmacological reason at the lower doses.

In the first few weeks (and again after each increase) nausea is the most frequently reported effect. It affects a substantial proportion of patients, particularly after meals that are larger or fattier than usual. Vomiting, loose stools or constipation, indigestion and burping are also common during this settling-in period. The NHS semaglutide medicines page describes these as typically mild to moderate and notes they usually improve within the first few weeks at a new dose.

One practical habit that many patients find genuinely useful: check the injection site briefly after each dose, a small area of redness or firmness is normal and settles on its own, but rotating between the abdomen, thigh and upper arm reduces the chance of localised reactions accumulating. It takes under a minute and keeps the skin comfortable across the full treatment period.

Fatigue, mild headache and dizziness appear less consistently but are reported by some patients, particularly early on. These generally resolve without any change to treatment.

Step 2: the side effects that need a call to your GP or prescriber

A smaller group of side effects associated with Wegovy's broader side-effect picture are not dangerous for most people but do warrant a conversation with your prescriber if they persist or worsen.

Heartburn that does not respond to simple antacids, persistent nausea or vomiting that is preventing adequate fluid intake, and signs of dehydration (dark urine, dizziness on standing, reduced urination) all fall into this category. Your prescriber may recommend slowing down the titration schedule, adjusting meal composition, or temporarily pausing a dose increase, decisions that should always be made with clinical input, not based on what worked for someone in an online forum.

Hair thinning is reported by some patients on GLP-1 medicines during rapid weight loss. It is generally a consequence of the calorie deficit and nutritional shift rather than a direct drug effect, and tends to reverse as the body adapts. It is still worth mentioning to your prescriber at a review, particularly if it is significant. Explore the broader safety considerations for Wegovy for more detail on less common effects.

Step 3: symptoms that need urgent medical attention

Acute pancreatitis is a known but uncommon risk with GLP-1 receptor agonists. In January 2026, the MHRA issued a Drug Safety Update specifically highlighting this risk across the class, the symptom to act on immediately is severe, persistent stomach pain, especially if it spreads toward the back, with or without vomiting. This is not typical nausea; it is a qualitatively different, more intense pain that does not ease. Stop the injection and seek urgent medical care without delay. You can read the MHRA's Yellow Card portal for further detail on how this and other serious reactions are monitored and reported.

Other symptoms warranting urgent assessment include signs of a serious allergic reaction (facial swelling, difficulty breathing, severe rash), gallbladder-related pain (sharp pain in the upper right abdomen, particularly after eating), and any sudden changes in vision. Patients who want a fuller picture of the safety concerns associated with semaglutide, including retinopathy risks for those with a relevant history, will find it worth reading before starting or if any new symptoms arise.

If you have concerns about any symptom and are unsure whether it warrants emergency care, the default is to seek advice promptly. The semaglutide safety overview covers the full contraindication list if you want to read further.

Who should be especially cautious

Wegovy is not suitable for everyone, and a thorough consultation exists precisely to identify situations that need extra care. People with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2 should not take semaglutide. Those with a past episode of pancreatitis, or certain inflammatory bowel conditions, require a careful prescriber discussion before starting.

As noted in NICE's appraisal of Wegovy (TA875), the medicine is recommended within a structured programme that includes diet and activity support, not as a standalone intervention. That context matters for safety as well as results: patients with appropriate support tend to manage side effects more effectively and to sustain the nutritional habits (adequate protein, hydration, fibre) that reduce the risk of side effects like constipation and hair thinning.

For questions about how Wegovy's safety profile looks over longer periods, or if you are weighing it against other options, our clinical team can help. Check your eligibility with a free consultation, our prescribers work through tolerability and individual risk factors as part of every assessment, not as an afterthought.