Wegovy jab side effects: separating the normal from the serious

The myth worth clearing up first: side effects don't mean the jab isn't working

A belief that crops up regularly is that if nausea or loose stools arrive, something has gone wrong, the dose is too high, the medicine isn't right, or the body is rejecting it. In almost every case, that's not what's happening. Semaglutide, the active medicine in Wegovy, slows the rate at which the stomach empties and acts on appetite signals in the brain. Those same mechanisms that reduce hunger also cause the gut to feel the change. Nausea in the first week or two after starting, or after a dose increase, is the body adjusting to a new hormonal signal, not a warning that treatment should stop. Prescribers titrate the dose gradually for exactly this reason: starting at 0.25mg before working up through 0.5mg, 1.0mg, 1.7mg and 2.4mg gives the system time to adapt at each step. It is worth letting go of the idea that a side-effect-free experience signals something is wrong, too; our guide to having no side effects on Wegovy explains why some people simply tolerate it well from the start. Neither pattern (symptoms or none) tells you whether the medicine is working therapeutically.

If you'd like a full picture of what to expect, our page covering side effects from Wegovy runs through the most commonly reported reactions across clinical trials and real-world use, including nausea, vomiting, diarrhoea, constipation, indigestion, burping, and fatigue. These effects tend to cluster in the days after a new dose. Headache and dizziness appear less frequently. Injection-site redness or mild bruising can occur and usually resolves within a day or two.

Side effects that need medical attention, and the ones that need it urgently

Most of what people experience on the Wegovy jab does not require a trip to A&E or an urgent GP call. Persistent nausea that disrupts daily life, or constipation lasting more than a week, is worth raising with your prescribing team, but it's not an emergency. The picture changes with a specific cluster of symptoms. Severe, persistent abdominal pain that reaches through to the back, with or without vomiting, can indicate acute pancreatitis. The MHRA Drug Safety Updates for GLP-1 receptor agonists flag this as an infrequent but serious risk: if this pain arrives, seek medical help the same day rather than waiting to see if it passes. Pancreatitis is rare, but it's the reason prescribers ask about any history of the condition before starting treatment.

Other symptoms that warrant prompt review: signs of a severe allergic reaction (swelling of the face or throat, difficulty breathing, widespread rash appearing quickly); symptoms suggesting gallbladder problems (sharp upper-right abdominal pain, particularly after eating fatty food); and signs of significant dehydration following repeated vomiting or diarrhoea, persistent dark urine, dizziness on standing, or no urine output over several hours. If you're on insulin or certain diabetes medicines alongside Wegovy, low blood sugar is also a risk worth knowing about. Call 111 or your GP if you're unsure; call 999 if symptoms are severe.

How side effects tend to change over time on the jab

The trajectory for most people is improvement. GI symptoms are usually worst in the first fortnight after any dose step, then ease as the body adjusts. By the time someone reaches and settles on their maintenance dose (2.4mg weekly, or the newer 7.2mg dose now approved in the UK) many find the symptoms that troubled them at lower doses have largely resolved. There are practical steps that help: smaller, lower-fat meals; eating slowly; staying well hydrated; avoiding lying down immediately after eating. These aren't fixes, but they reduce the intensity of GI effects for most people during the adjustment window.

For a closer look at how long specific symptoms typically last, our page on how long Wegovy side effects last goes through the timeline in more detail. If symptoms persist beyond a few weeks at a stable dose, or they're significantly affecting daily life, that's a conversation for your prescriber, not something to manage silently. The five most reported Wegovy side effects are also worth reviewing before you start, so nothing comes as a surprise.

Reporting side effects and getting clinical support

Two things are worth knowing about reporting. First, the NHS encourages patients to flag suspected side effects via the Yellow Card scheme, this is how safety signals get detected early, and it's open to patients as well as healthcare professionals. Second, your prescriber should always be your first call for anything that's affecting how you feel on treatment. Self-managing side effects without clinical input (especially for more than a short period) isn't the right approach for a prescription medicine.

At nume, every repeat order is reviewed by a GPhC-registered prescriber before it's dispensed; that review is the point at which side-effect concerns can be raised and dose decisions revisited. Aftercare support is available seven days a week via our clinical team. If you're wondering whether Wegovy is right for you given what you've read here, our prescribers cover suitability and likely side-effect profile as part of the free consultation, before any prescription is issued. There's no obligation. More general background on the treatment itself is on our Wegovy overview page, and a fuller breakdown of reported reactions is covered in our complete Wegovy side effects guide.