Side effects of Wegovy injections: what to expect and when to act

The side effects most people experience in the first few weeks

When you start Wegovy, your body is adjusting to semaglutide slowing the rate at which your stomach empties. That physiological shift is the reason nausea sits at the top of the side-effect list. Vomiting, diarrhoea, constipation, indigestion and burping are all part of the same picture. Fatigue, mild headaches and dizziness are reported less often but not unusually.

These effects tend to be most noticeable in the first few days after each injection, particularly after a dose increase. For the majority of people they soften considerably within one to two weeks. The titration schedule (starting at a low dose and stepping upward) exists largely to give your system time to adapt, which is why following your prescriber's plan rather than rushing the escalation makes a practical difference.

One thing worth doing each week: in the 24 hours after your injection, take a moment to check in on how you feel. If symptoms feel different from the usual adjustment pattern (more intense, longer-lasting, or involving new areas) note it down and flag it to your clinical team. That brief self-check can catch something early that might otherwise be dismissed. The first injection in particular tends to prompt the most questions, and knowing what is typical versus what warrants a call takes a lot of the uncertainty away.

Injection-site reactions (mild redness, swelling or itching at the spot you injected) are also common and nearly always temporary. Rotating between the abdomen, thigh and upper arm, and cleaning the skin beforehand, reduces the frequency.

Side effects that need urgent medical attention

Most Wegovy side effects are manageable, but some require you to stop and seek help the same day. Knowing them in advance is not alarming; it is practical.

Acute pancreatitis is rare, but the MHRA issued a specific Drug Safety Update in January 2026 drawing attention to it across GLP-1 medicines including semaglutide. The symptom to act on is severe, persistent abdominal pain that radiates toward your back, with or without vomiting. If that happens, stop taking the injection and get medical attention straight away. Gallbladder problems, including gallstones and inflammation, have also been reported; symptoms typically include sharp upper-right abdominal pain, sometimes accompanied by fever or jaundice.

Severe dehydration from prolonged vomiting or diarrhoea can affect your kidneys, particularly if you are not managing to keep fluids down. Signs of dehydration to take seriously: significantly reduced urination, dizziness that does not pass when you sit or lie down, or confusion.

Allergic reactions are uncommon but possible, facial swelling, difficulty breathing or a severe skin rash are reasons to call 999. Heart rate increases have been reported in clinical trials. Anyone with a history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2 should not use this medicine; your prescriber will have screened for these during your consultation. The full profile of semaglutide injection side effects covers these in more depth alongside practical guidance on each.

If you are ever unsure whether what you are experiencing warrants attention, the safest approach is to contact a clinician rather than wait. Our team is available seven days a week.

How the risk picture changes with dose and individual factors

Not everyone's experience of Wegovy looks the same. The dose you are on, how quickly you titrated, other medicines you take and your own health history all shape what you are likely to feel.

People who move through the dose steps slowly tend to report fewer and milder GI effects. That is not just anecdote, it is consistent with how the medicine works. If a particular dose step causes significant nausea, staying at it for longer before progressing is a conversation worth having with your prescriber rather than pushing through.

Drug interactions are another variable. Wegovy slows gastric emptying, which can affect how quickly oral medicines are absorbed. If you take a daily oral contraceptive pill, this is worth discussing with your prescriber before you start, since absorption timing may be affected. The same applies to any other time-sensitive oral medication.

People with a history of eating disorders, pancreatitis, or significant gallbladder disease need a careful clinical conversation before starting. Those who are pregnant, breastfeeding or actively trying to conceive should not use Wegovy; the medicine is also not licensed for under-18s. None of these are reasons to rule yourself out without a consultation, they are reasons why the assessment matters. You can read a broader overview of the side effects associated with semaglutide weight-loss injections to see how this profile fits into the wider picture.

Reporting side effects and getting support

The UK's Yellow Card scheme, run by the MHRA at yellowcard.mhra.gov.uk, lets anyone (patient or carer) report a suspected side effect from any medicine including Wegovy. These reports genuinely feed into ongoing safety monitoring; they are not lost in a system. If you experience something unexpected, reporting it is a straightforward thing to do and takes about ten minutes.

At nume, side-effect support is part of the service, not an optional extra. Every patient has access to our clinical team seven days a week for aftercare questions, and every repeat prescription goes through a clinical re-review, your prescriber looks at how treatment has gone before the next pen is dispensed. The NHS patient information page for semaglutide is also a reliable reference you can bookmark for ongoing use.

If you are weighing up whether Wegovy is right for you, or you have questions about how your own health history might shape your experience of it, speaking to our prescribers through a free consultation is the place to start. That conversation covers suitability, side effects and your individual circumstances, properly, not generically. If you are also considering other options in this class of treatment, our guide to weight loss injections including Ozempic sets out how the available medicines compare.