Wegovy side effects: how common they are and the warning signs

Four trials, 2,650 adults, 68 weeks of follow-up: that is the basis on which the Summary of Product Characteristics for Wegovy (semaglutide) counts its adverse reactions. The document is public, the UK version is kept up to date under the MHRA's oversight, and it answers with unusual precision the question anyone newly prescribed the jab is asking: Wegovy side effects, which ones, and how often?

One detail changes how the figures read. The trials compared the medicine with a placebo, and the placebo group also had nausea, diarrhoea and stomach aches. The gap between the two columns is what really belongs to the treatment.

The most common Wegovy side effects

They are digestive, and they affect a lot of people. The product information classes nausea, vomiting, diarrhoea, constipation and abdominal pain as "very common", meaning they affect more than 1 person in 10. The proportions recorded over the 68 weeks of the trials are well above that threshold.

These percentages count anyone who had at least one episode in more than a year. The same document specifies that most episodes were mild to moderate and short-lived, with constipation the exception for how long it lasted.

Headache and fatigue complete the list of "very common" effects. For this whole group the product information adds that they are seen mainly during the dose-escalation period, the sixteen weeks in which the weekly dose climbs from 0.25mg to 2.4mg.

How many people give up? Across the four trials, digestive problems led 4.3% of participants to stop for good. In the STEP 1 trial alone, run in 1,961 adults without diabetes and published in the New England Journal of Medicine in 2021, the proportion was 4.5%, against 0.8% on placebo.

Hair, skin, taste: the ones people do not expect

The "common" category, up to 1 person in 10, holds the lesser-known effects.

Hair loss was reported by 2.5% of treated participants and 1.0% of those on placebo. It was mostly mild, more frequent in people who had lost at least 20% of their weight, and most recovered without stopping treatment. That pattern points to the weight loss as much as to the drug, the same logic that lies behind the hollowed look discussed in our article on Ozempic face.

More surprising is a change in skin sensation: sensitive skin, pain on touch, a burning feeling. It affected 2.1% of treated participants against 1.2% on placebo, with recovery in most cases. The UK product information notes that it becomes far more frequent at the higher 7.2mg dose now licensed for some adults with obesity, where it was reported by 21.6% of trial participants.

The same category includes altered taste, injection site reactions, bloating, wind, reflux, and dizziness, which occurs mainly while the dose is being increased and matters for anyone who drives.

Gallstones belong to this group as well. They were reported in 1.6% of treated participants, and led to inflammation of the gallbladder in 0.6%.

Less frequent again, up to 1 person in 100: low blood pressure, feeling light-headed on standing, a faster pulse, kidney stones. The trials measured a mean rise of 3 beats per minute.

Rare, and to be taken seriously

Setting aside the complications specific to diabetes, a handful of serious effects appear in the product information.

Acute pancreatitis is classed as "uncommon". In the phase 3 trials it was confirmed in 0.2% of participants on semaglutide and fewer than 0.1% on placebo. In January 2026 the MHRA strengthened the warning for the whole class of GLP-1 medicines, after reviewing Yellow Card reports that included rare necrotising and fatal cases.

Severe allergic reactions are "rare", up to 1 person in 1,000.

Non-arteritic anterior ischaemic optic neuropathy, or NAION, was added as a "very rare" effect after a European review that concluded in June 2025. It can cause loss of vision in one eye, without pain.

Bowel obstruction is listed with a frequency "not known", from reports made after the medicine went on sale.

The UK document also records a finding from SELECT, the large cardiovascular trial: more fractures of the hip and pelvis on Wegovy than on placebo among women (1.0% against 0.2%) and among people aged 75 and over (2.4% against 0.6%). Hip fracture is classed as "rare" overall.

When to get help straight away

The leaflet leaves no room for interpretation on these points.

Severe, persistent pain in the stomach area, which may move through to the back, means seeking urgent medical attention: it is the possible sign of pancreatitis. Difficulty breathing, rapid swelling of the face or throat, a spinning head, a racing heart or collapse: call 999. Sudden loss of vision or eyesight that deteriorates quickly is a reason to contact a doctor immediately. Severe constipation with pain, bloating and vomiting also needs prompt medical advice. If you are unsure how urgent something is, NHS 111 can direct you.

Where the product information asks for caution

Some people need to talk things through with their prescriber before and during treatment.

In people with type 2 diabetes, combining Wegovy with a sulfonylurea or insulin raises the risk of hypos: in the STEP 2 trial, clinically significant hypoglycaemia was seen in 6.2% of treated participants against 2.5% on placebo. People with diabetic eye disease need close monitoring while on semaglutide.

A stomach that already empties slowly, a condition called gastroparesis, means a risk of more severe digestive effects. Fragile kidneys make dehydration more dangerous. A planned anaesthetic is a reason to mention the treatment. Pregnancy is excluded: the product information asks for contraception during treatment and for Wegovy to be stopped at least two months before a planned pregnancy, and the MHRA advises against use while breastfeeding.

Wegovy also carries the black triangle given to medicines under additional monitoring. In practice that means every suspected side effect is worth reporting through the Yellow Card scheme, which patients can use themselves.

What food can do, and what it cannot

It does not correct a side effect. It can make the first weeks more comfortable.

The one instruction in the product information concerns fluids: take care not to become dehydrated when vomiting or diarrhoea strike. The other pointers are those clinicians commonly give anyone who digests slowly: smaller portions, unhurried meals, a pause as soon as hunger goes, fewer fatty or very large dishes on nauseous days. Our GLP-1 diet guide covers them, and alcohol is dealt with separately in Mounjaro and alcohol, which applies to Wegovy too.

If eating or drinking becomes difficult for several days in a row, your prescriber or pharmacist is the person to speak to. To place Wegovy within its family of medicines, our guide to GLP-1 side effects sets the product information for each side by side, and Mounjaro side effects has its own article.

Frequently asked questions

What are the most common side effects of Wegovy?

Nausea, reported by 43.9% of trial participants, then diarrhoea, vomiting, constipation and abdominal pain. The product information also classes headache and fatigue as very common.

How long do Wegovy side effects last?

Most digestive episodes are short and occur while the dose is being increased, according to the product information. Constipation tends to last longer. Symptoms that persist or stop you eating and drinking should be reported to your prescriber.

Does Wegovy cause hair loss?

It is a recognised effect, classed as "common": 2.5% of treated participants reported it, against 1.0% on placebo. It was more frequent in people who had lost a lot of weight, and most recovered while continuing treatment.

Do Wegovy and Ozempic have the same side effects?

They contain the same molecule, semaglutide, and their product information is very similar. The frequencies differ because the doses, licensed uses and trial populations are not the same: Ozempic is a treatment for type 2 diabetes.

Can Wegovy affect your mood?

Cases of suicidal thoughts have been reported with this class of medicines. The European Medicines Agency's safety committee concluded in April 2024 that the data did not establish a causal link. Any unusual change in mood should be raised with your doctor.

This article is for information only and is no substitute for advice from a healthcare professional. Never change your treatment without talking to your doctor.