Side effects of the Wegovy injection: what the evidence says

Where the data on Wegovy's side effects comes from

The clearest picture of Wegovy's tolerability comes from the STEP 1 trial, a 68-week randomised controlled study published in the New England Journal of Medicine. Participants on semaglutide 2.4mg reported gastrointestinal events at substantially higher rates than those on placebo, nausea, vomiting, diarrhoea and constipation were the main findings. That signal has been consistent across the STEP programme and is reflected in the product's UK prescribing information. The NHS medicines page for semaglutide lists these in plain language for patients. Knowing they are expected, documented and usually transient is useful framing before a first injection. The MHRA continues to monitor the medicine under its Black Triangle (▼) status, which means post-market safety data are collected and reviewed on an ongoing basis.

For most people, the side-effect burden is front-loaded. The slow titration schedule (starting at 0.25mg before working up toward the 2.4mg maintenance dose) exists precisely to give the body time to adjust. If you want a detailed breakdown of what semaglutide injection side effects to expect at each stage, that page covers the full picture. Side effects tend to cluster in the day or two after an injection and are usually less noticeable by the end of the week.

The gastrointestinal effects in practice

Nausea is by far the most commonly reported complaint. It tends to arrive within a few hours of an injection and typically lessens over the following days. Vomiting, diarrhoea and constipation are also well-documented; indigestion, bloating and burping appear less frequently but are recognised. Fatigue and headache round out the common list.

Practical steps that many patients find helpful include eating smaller portions, choosing blander foods during the first week of a new dose, staying well hydrated, and slowing down at mealtimes. These are not dosing instructions, your prescriber and the Patient Information Leaflet that comes with your pen are the right places for personalised guidance. It is worth knowing that a dose increase often brings a brief return of symptoms even if the previous dose was well tolerated. A question our prescribers hear fairly often is whether to delay a dose increase because of a holiday or a busy patch at work; that kind of timing consideration is exactly what the follow-up aftercare is there to discuss. You can reach our support team seven days a week.

Injection-site reactions (localised redness, a little swelling or mild bruising) are common and nearly always resolve on their own. Rotating sites between the abdomen, thigh and upper arm, and using a fresh needle each time, reduces the chance of skin irritation. If you want to read more about the first injection specifically, what to expect from your first Wegovy injection covers that period in detail.

When to get medical help

Most side effects are manageable and self-limiting, but some require prompt attention. The MHRA's January 2026 Drug Safety Update flagged acute pancreatitis as an infrequent but serious risk with GLP-1 medicines. The symptom to act on quickly is severe, persistent abdominal pain that may radiate through to the back, with or without vomiting. Stop the injection and seek urgent medical care, do not wait for your next planned appointment.

Other situations that need prompt review include signs of a serious allergic reaction (facial swelling, difficulty breathing, rapid heartbeat), symptoms suggesting significant dehydration from prolonged vomiting or diarrhoea, and gallbladder symptoms such as pain in the upper-right abdomen, particularly after eating. Mood changes or thoughts of self-harm are rare but documented in post-market surveillance for GLP-1 medicines; if these occur, speak to a healthcare professional straight away.

Suspected side effects can be reported to the MHRA via the Yellow Card scheme at yellowcard.mhra.gov.uk. This matters: Yellow Card reports from real patients are part of how post-market safety signals get identified and acted on.

How nume's prescribers approach this before treatment starts

At nume, a GPhC-registered Independent Prescriber reviews your consultation before any treatment is issued. That review covers your medical history and current medicines, relevant because some conditions and combinations call for extra caution. Patients who want to understand the side effects of weight loss injections using semaglutide before committing to treatment will find a thorough breakdown on that page. Patients also often ask about storage, and if you are unsure about what temperature to store Wegovy at, getting that right from the start helps protect the medicine's effectiveness. If you are curious how Wegovy sits in the wider landscape of injectable weight-loss treatments, our treatment overview is a good starting point.

Safe prescribing is not just a box to tick at the start. Every repeat order at nume is re-reviewed clinically. If side effects are affecting your daily life or you are unsure whether something you are experiencing is treatment-related, the right move is to talk to a prescriber rather than guess. For a comprehensive guide to what the side effects of Wegovy injections are, including how common each one is and what to do about them, that resource is worth bookmarking before you begin. Patients switching from or comparing products may also find it helpful to read about the side effects of Ozempic semaglutide injection, since the active ingredient is the same even though the licensed use differs. Start with a free consultation if you have not yet been assessed, our prescribers discuss tolerability and suitability as part of that first conversation, not as an afterthought.