What Are the Side Effects of Wegovy, and When Should You Act?

Step 1: What most people notice in the first few weeks

The side effects most closely linked to Wegovy cluster around digestion. Nausea tops the list; it tends to arrive within a day or two of each injection and usually fades over three to five days. Vomiting, burping, indigestion, bloating and loose stools can accompany it, particularly at the lower starting doses when the body is still adjusting. Constipation sits at the other end of that spectrum and affects some people more than nausea does.

Tiredness and headache are reported less often but are recognised reactions, especially in the early weeks. Injection-site redness or mild itching is also possible; rotating between the abdomen, thigh and upper arm from one week to the next tends to reduce this. The common side effects of Wegovy described in the Patient Information Leaflet match this pattern closely.

One practical habit that costs almost nothing: before each weekly injection, run through a quick mental check of how your stomach and energy have felt over the past few days and note anything unusual. That 30-second review makes it far easier to spot a pattern if something changes, and gives you useful detail if you need to contact your prescriber.

The NHS medicines page for semaglutide lists these effects clearly and explains which are expected versus which require attention.

Step 2: How side effects typically change as your dose increases

Wegovy is titrated gradually — starting at 0.25 mg and moving upward roughly every four weeks — precisely because the gut needs time to adapt. Each dose step can bring a brief return of nausea or loose stools, even for people who had already settled on their previous dose. This is not a sign that the medicine has stopped agreeing with you; it is the normal adjustment window repeating.

The pattern means the weeks immediately following a dose increase deserve a little extra attention. Eating smaller meals, avoiding rich or fatty food during those first few days, and staying well hydrated are all steps your prescriber or the Patient Information Leaflet will cover. For a fuller picture of how reactions change across the dosing ladder, the page on what to expect when taking semaglutide covers this in more detail.

Hair thinning is occasionally reported during rapid weight loss on any treatment (including Wegovy) and is generally linked to the physiological stress of losing weight quickly rather than the medicine itself. It tends to resolve. Gallbladder-related symptoms, including gallstones, are a recognised risk with significant weight loss; tell your doctor if you develop upper abdominal pain, particularly on the right side, with or without nausea.

If you are also exploring how semaglutide interacts with other aspects of your health, the page on Wegovy and liver-related effects addresses that specific question separately.

Step 3: Symptoms that need prompt or emergency medical attention

A small number of side effects are serious enough that waiting is the wrong move. Knowing this list before you start is genuinely useful.

Acute pancreatitis is the most clinically significant. In January 2026, the MHRA's Drug Safety Update for GLP-1 receptor agonists specifically flagged this risk: severe and persistent stomach pain that spreads towards the back, with or without vomiting, is the key warning sign. Stop treatment and get same-day medical help. Do not wait to see if it settles.

Other situations that warrant urgent assessment include: signs of a serious allergic reaction (swelling of the face, lips or throat; difficulty breathing; rapid heartbeat); symptoms of significant dehydration after prolonged vomiting or diarrhoea (feeling faint, passing very little urine, extreme dry mouth); and, in people with diabetes, symptoms of low blood sugar if Wegovy is used alongside insulin or a sulphonylurea. Low mood or thoughts of self-harm, while uncommon, should also prompt contact with a healthcare professional promptly. A deeper look at the most serious Wegovy side effects explains each of these in context.

If a symptom concerns you and it is not on a list anywhere, trust that concern. Contact your prescriber, your GP, or NHS 111. For anything that feels severe and sudden, call 999 or go to A&E.

Suspected side effects (including reactions you are unsure about) can be reported at yellowcard.mhra.gov.uk. Wegovy carries the Black Triangle (▼) status, which means the MHRA actively encourages reporting to build the safety evidence base.

Who discusses side effects with you at nume

At nume, every consultation is personally read by a GPhC-registered Independent Prescriber (a real clinician, not an automated system) on the same day you submit it. Side effects, your medical history and any other medicines you take are all part of what they assess before any prescription is issued. There are no auto-renewals; each repeat order goes through the same clinical review, so changes in how you are tolerating treatment are caught.

If you have questions about whether Wegovy is appropriate for you, our prescribers talk through suitability and side effects as part of the free consultation process. You can check your eligibility and start a free consultation on our treatment page. For a broader overview of how the medicine works, the Wegovy information page covers the full picture.