Reactions to Wegovy: what's normal, what's not, and when to call for help

Which reactions to Wegovy do most people actually get?

The honest answer is that the gut bears most of it. Nausea tops the list by some distance, followed by vomiting, diarrhoea, constipation, indigestion and burping. Fatigue and headache show up less often but are well-documented. These reactions to semaglutide happen because the drug slows the movement of food through your stomach — the same mechanism that reduces appetite also means your digestive system is adjusting to a new pace.

For most people the timing follows a pattern. Symptoms are most noticeable in the days after an injection, particularly just after starting or after a dose step. By the second or third week at that level they have usually quietened. That is not a guarantee (some people find certain doses sit less easily than others) but it is the most common course.

Practical things that genuinely help: eating smaller portions, avoiding very fatty or rich food, staying well hydrated, and not lying down immediately after eating. If loose stools become persistent rather than an early blip, our page on persistent diarrhoea on Wegovy covers what to watch for. Constipation at the other end of the spectrum is also common; there is separate guidance on managing constipation on Wegovy that your prescriber can point you towards as well.

What do injection-site and skin reactions to semaglutide look like?

A question our prescribers hear most weeks is whether a patch of redness, itching or a small lump at the injection site is something to worry about. Usually it is not. Local reactions at the site (redness, warmth, mild swelling or itching lasting a day or two) are documented in the clinical data and tend to resolve without intervention. Rotating your injection site each week (abdomen, thigh and upper arm are all suitable) reduces the likelihood of repeated localised irritation.

Wegovy skin reactions that spread beyond the injection site, or that develop across the trunk or face, are a different matter. Hives, a spreading rash, or skin that feels hot and swollen in a larger area may signal an allergic response rather than a simple local reaction. Our page on Wegovy skin reactions goes into more detail on distinguishing the two. If you are unsure whether what you are seeing is local irritation or something wider, your prescriber is the right first call.

True systemic allergic reactions to semaglutide are uncommon but not unheard of. Signs of a serious allergic reaction (swelling of the face, lips, tongue or throat, difficulty swallowing or breathing, a rapid heartbeat alongside a widespread rash) need emergency care immediately, not a call to a pharmacy. Call 999 or go to A&E. For a fuller picture of what an allergic response to this medicine can involve, see our page on allergic reactions to semaglutide.

When does a reaction to Wegovy need urgent medical help?

The MHRA's January 2026 Drug Safety Update for GLP-1 medicines drew specific attention to acute pancreatitis. The symptom profile to recognise: severe pain in the upper abdomen that may travel through to the back, which does not settle quickly and may come with vomiting. If that description fits what you are feeling, stop the injection and get medical help the same day, do not wait to see if it passes. Pancreatitis is not common on Wegovy, but it can be serious, and early assessment matters.

Gallbladder problems are another reason to seek prompt attention. Intense pain in the upper-right abdomen, fever, or jaundice (yellowing of the skin or whites of the eyes) can indicate gallstones or cholecystitis, both of which have been reported with GLP-1 medicines. Severe or repeated vomiting and diarrhoea can also lead to dehydration quickly enough to affect kidney function, so if you cannot keep fluids down for more than a day, that is a reason to contact your GP or 111 rather than pushing through.

Other reactions worth a same-day call or 111 consultation: signs of a serious allergic response as described above; sudden changes in vision (particularly relevant for anyone with diabetic eye disease); and any new or worsening low mood or thoughts of self-harm, which should always be taken seriously. A full run-down of less common but documented reactions sits on our Wegovy side effects page, including what the clinical trial data recorded for each.

If you experience what you believe is an adverse reaction to Wegovy, you can report it through the Yellow Card scheme directly. Reports from patients and carers feed into the MHRA's ongoing safety monitoring and are genuinely useful.

How does a prescriber weigh up these risks before recommending Wegovy?

Wegovy is not prescribed in a vacuum. A prescriber reviewing a consultation considers your medical history, current medications, and any conditions that would change the risk profile, history of pancreatitis, certain gallbladder conditions, and a personal or family history of medullary thyroid cancer are among the factors that would alter the clinical picture. The licensed indication covers adults with a BMI of 30 or above, or 27 and above with at least one weight-related condition; lower thresholds can apply for some ethnic backgrounds under UK guidance.

At nume, that review happens the same day your consultation comes in. A GPhC-registered Independent Prescriber reads it personally; a bot does not make the call. Side effects and how to manage them are part of what that clinical conversation covers. If you would like our prescribers to assess whether Wegovy is suitable for you, and to talk through what reactions are most likely at your starting dose, the right place to start is a free consultation. For more background on the medicine itself, the Wegovy overview covers licensing, how it works, and what the trial evidence says.