When Do You Feel Side Effects of Wegovy?

When do Wegovy side effects usually hit after the first injection?

The short answer is: fairly quickly. Most people who experience nausea or digestive discomfort after their first Wegovy injection notice it within a few hours of the dose, with the peak often arriving the following morning. The NHS medicine information page for semaglutide lists nausea, vomiting, diarrhoea and constipation as the most common reactions, and this pattern is well established from the STEP 1 trial data and routine clinical use.

The starting dose (0.25 mg) is deliberately low. Its job is to let your gut adapt to the medicine before the dose rises, so side effects at this stage are generally mild. That said, even mild nausea can be a surprise if you weren't expecting it, and our page on when Wegovy side effects start explains exactly what to expect and why the timing works the way it does. Eating smaller meals, avoiding rich or fatty food on injection days, and drinking plenty of water all help. Timing your injection in the evening means you sleep through the worst of it, a small but genuinely useful trick many patients mention. If you're planning around something important, like a holiday or a run of busy work weeks, it's worth raising that with your prescriber before you start, so you can pick an injection day that suits your schedule.

For a closer look at the very early hours of treatment, our page on how soon Wegovy side effects appear goes into more detail.

Do side effects come back every time the dose increases?

Often, yes. This is one of the most useful things to know, and one of the things patients tell us they wish they'd been told upfront. Wegovy follows a step-by-step titration: 0.25 mg, then 0.5 mg, then 1.0 mg, then 1.7 mg, then 2.4 mg (and now up to 7.2 mg with the MHRA-approved higher-dose pen). Each step up is a fresh signal to the gut. Side effects that had quietened down at the previous dose can resurface for a week or so after the increase, then settle again.

This pattern repeats because semaglutide slows gastric emptying and acts on GLP-1 receptors in ways that take time for the body to recalibrate to at each new level. It's not a sign that the medicine is failing or that something is wrong; it's the expected arc. Knowing this in advance means you can plan around a dose-change week rather than being blindsided by it.

Our page on how long Wegovy side effects last covers what's typical at each stage of the titration in more detail. The full Wegovy side effects guide is also worth reading before you start treatment.

When do side effects usually ease off?

For most people, nausea and other GI symptoms peak in the first five to seven days of a new dose and fade noticeably by the end of week two. A smaller group find they persist at a low level for the duration of treatment, particularly at higher doses, this is less common but not unusual, and it's something to discuss with your prescriber rather than simply tolerate in silence.

Constipation tends to follow a different timeline; it can develop gradually over weeks rather than appearing acutely after an injection. Staying hydrated and keeping fibre intake up helps considerably. Fatigue and mild headaches are also reported, especially early on, and usually resolve as the body adjusts.

One thing worth knowing: if you stop Wegovy and then restart, or restart after a break of more than a few weeks, the side-effect clock resets. Your prescriber will usually advise going back to a lower dose, not continuing where you left off. Our page on side effects when you stop Wegovy explains what to expect in that situation.

Which side effects need urgent medical attention?

The vast majority of Wegovy side effects are unpleasant rather than dangerous, and they ease with time. A few, though, require prompt action. In January 2026 the MHRA issued a Drug Safety Update reminding healthcare professionals and patients that acute pancreatitis is a known, infrequent but serious risk with GLP-1 medicines. The warning sign to act on is severe, persistent abdominal pain that radiates into your back, with or without vomiting. Don't wait to see if it passes, seek urgent medical help.

Other situations that warrant prompt attention include signs of dehydration from persistent vomiting or diarrhoea (dark urine, dizziness, very little output), symptoms suggesting a gallbladder problem (pain in the upper right abdomen, especially after eating), and any allergic reaction such as swelling of the face, lips or throat. Low mood or thoughts of self-harm are listed in the prescribing information and should be taken seriously.

If something doesn't feel right, contact your prescriber, call 111, or go to A&E for anything severe. You can also flag suspected side effects directly through the MHRA Yellow Card scheme, this reporting helps regulators monitor medicines in real-world use. Our clinical team at nume provides 7-day aftercare, so you're never dealing with unexpected symptoms on your own. To find out more about what the full treatment journey looks like, visit our Wegovy overview page.