Taking Wegovy when sick: a practical guide

Step 1: judge how sick you actually are before touching your pen

Not every sniffle or dodgy evening warrants a change to your injection schedule. A cold, a minor throat infection or a day of low appetite on top of Wegovy's usual appetite suppression is unlikely to require you to adjust anything. What does warrant attention is the severity of your gut symptoms, because semaglutide already slows the rate at which your stomach empties. Lay nausea on top of that and it compounds quickly.

Run through three checks before your next injection day arrives. First: can you keep fluids down? Second: have you had persistent vomiting or diarrhoea for more than 24 hours? Third: do you feel lightheaded, have a dry mouth, or notice your urine has turned dark? If the answer to any of those is yes, your body is under enough stress that adding a dose that further slows gastric emptying may make things worse, not better. The NHS semaglutide guidance flags dehydration from prolonged gastrointestinal illness as a specific concern on GLP-1 treatment.

If you feel rough but functional (keeping food and water down, no signs of dehydration) carry on with the normal schedule, take things gently with food, and monitor. Plenty of people inject on a day they feel below par without incident.

Step 2: know what to do if vomiting or diarrhoea is the main problem

This is where the practical rules get firmer. Persistent vomiting means your body is losing fluid faster than you can replace it, and the kidneys are the first organ to feel that pressure. Wegovy does not directly damage the kidneys, but dehydration on any medicine can reduce kidney function temporarily, something that the NHS England guidance on weight-management injections specifically highlights as a reason to pause treatment and seek advice.

The practical steps here are straightforward. Stop the planned injection until you can hold fluids reliably. Sip water, diluted squash or an oral rehydration solution steadily rather than gulping large amounts. If you cannot keep fluids down for more than a few hours, or if you feel confused, very weak or faint, that is a call to 111 or, in an emergency, 999. Do not sit it out.

For diarrhoea specifically, duration matters enormously. A single loose day is not the same as three days of significant fluid loss. If you want a clearer picture of how long GI disruption typically lasts on semaglutide treatment, the detail is covered on a separate page about how long diarrhoea lasts when taking Wegovy.

Once you are reliably keeping food and water down for 24 hours, you can generally resume your normal weekly schedule. If your injection day has passed during that window, contact your prescriber for guidance on the best timing to restart rather than doubling up.

Step 3: recognise the symptoms that go beyond ordinary illness

There is a small set of symptoms that should stop you entirely and prompt immediate medical contact, regardless of whether you associate them with being sick or with the medicine.

Severe, persistent stomach pain that radiates to the back (particularly if accompanied by vomiting) can be a sign of acute pancreatitis, which the MHRA flagged as an infrequent but serious risk in a January 2026 Drug Safety Update covering GLP-1 medicines. This is not the normal nausea of starting treatment; it is a different quality and location of pain. Call 999 or go to A&E. Similarly, signs of a serious allergic reaction (swelling of the face, lips or throat, difficulty breathing) require an ambulance, not a wait-and-see approach. Both of these are covered in the broader Wegovy side effects resource if you want the full picture, and if you would like to understand what reactions are considered typical versus serious before you start, there is a dedicated page on the side effects of taking Wegovy that walks through each one in plain language.

You can report any suspected side effects, whether you think they are caused by your illness or by the medicine itself, using the MHRA's Yellow Card scheme. It takes minutes and helps build the safety evidence base for everyone on this treatment.

Step 4: plan ahead so illness does not catch you off-guard

One thing patients often mention is that illness tends to strike at the worst possible time, a bank holiday, mid-December, or the week a new pen is due to arrive. If your delivery is expected and you are too unwell to manage it, contacting your pharmacy early means an alternative arrangement can usually be made. At nume, sorry, at nume, aftercare is available seven days a week, so a sick-day question does not have to wait until Monday.

Keeping a small written note of your injection days and dose helps too. If your illness means you are genuinely unsure whether you injected or not, do not inject again to be safe, contact your prescriber. For a broader look at what happens when semaglutide makes you feel unwell in general, the pages on Wegovy making you sick and feeling sick on Wegovy cover the mechanisms and management in more depth.

If you are considering starting Wegovy and want to understand how the full clinical assessment works, including how your health history is reviewed before any prescription is issued, the treatment overview at nume sets out the process clearly. And if cost is on your mind alongside the clinical questions, there is a plain-English breakdown on the Wegovy pricing page.