A lump after your Wegovy injection: causes, what's normal, and when to act

What the evidence and prescribing guidance say about injection-site reactions

When Wegovy was studied in the STEP clinical programme, injection-site reactions were documented as a known adverse effect across the trial population. The NHS semaglutide information page groups these reactions (including localised redness, swelling, itching and small nodules) under common side effects, meaning they affect roughly 1 in 10 users or more. That figure covers the full range of reactions, from a barely-noticeable firmness to a more obvious raised bump.

The lump itself is usually a localised subcutaneous response. When a small volume of fluid is deposited under the skin, the surrounding tissue can respond with mild inflammation, creating that familiar raised, sometimes tender area. It is not the medicine failing to work, and it does not mean the injection was given incorrectly in any dramatic sense. If you want to understand more about what this looks like in practice, our page on what to expect from a lump after injecting Wegovy covers the topic in detail. It means the tissue is reacting in a way it is well documented to react.

One misconception worth setting aside gently: a lump at the injection site is not a sign that the dose has been lost or that you need to re-inject. The medicine has been delivered. Re-injecting into a reactive site would add further irritation without benefit, and the Patient Information Leaflet is clear that a missed dose means waiting until the next scheduled day, not repeating on the same day.

Why lumps appear, and why the same spot is the real culprit

There are two main mechanisms behind persistent or recurring injection-site lumps. The first is acute local inflammation: the physical act of breaking the skin and depositing fluid triggers a brief immune response. This usually resolves within a few days and leaves nothing behind.

The second, more stubborn cause is lipohypertrophy, a build-up of fatty tissue that develops when the same small patch of skin absorbs repeated injections over weeks or months. The tissue thickens, becomes firmer, and may form a noticeable nodule that persists well beyond the post-injection window. Lipohypertrophy is more commonly discussed in the context of insulin injections for diabetes, but the principle applies equally to any subcutaneous injection given regularly. If you find yourself automatically reaching for the same spot on your abdomen every Friday, that habit is the likely explanation for a lump that won't fully disappear.

Technique matters too. Injecting into an area that is bruised, scarred or already showing a previous reaction slows absorption and prolongs local irritation. Using a fresh needle for each injection and keeping the pen at room temperature for a short period before injecting can reduce the sting and the tissue response. For guidance on needle hygiene, replacement needles and site-cleaning swabs are practical accessories worth having to hand.

Rotating sites properly means cycling through the three approved areas (abdomen (avoiding a 5 cm radius around the navel), thigh and upper arm) and within each area, picking a slightly different spot each week. A simple personal rotation map, jotted on paper or tracked in a notes app, can make the habit automatic.

Signs that a lump needs medical attention

The vast majority of Wegovy injection-site lumps are a nuisance, not a danger. But a small number of features should prompt you to contact a healthcare professional rather than waiting.

Get in touch with your prescriber or GP (or seek urgent care) if the lump is: growing larger rather than settling after 48–72 hours; warm or hot to the touch; surrounded by spreading redness; producing any discharge; or accompanied by a fever or general feeling of being unwell. These features could indicate a skin infection (cellulitis or abscess) that needs assessment and possibly antibiotics. Infections at injection sites are uncommon with clean technique, but they are not impossible.

An allergic reaction is a separate concern. Localised itching and a small raised weal are listed as common injection-site effects and are not a systemic allergy. A systemic allergic reaction (widespread rash, facial swelling, difficulty breathing, rapid heartbeat) is a medical emergency that needs 999. That pattern is rare with Wegovy, but knowing the distinction means you can respond proportionately rather than either dismissing everything or worrying unnecessarily. If you have questions about fatigue alongside your injection or other physical reactions, our prescribers are available seven days a week.

If you are uncertain whether what you're seeing is within the expected range, the MHRA Yellow Card scheme allows patients to report suspected side effects directly, and doing so contributes to the ongoing safety monitoring of the medicine.

Practical steps and when to speak to your prescriber

For a straightforward post-injection lump with no worrying features: leave it alone, apply a cool (not ice-cold) compress if it is tender, and avoid injecting into that spot until it has fully resolved. Most settle within a few days. Avoid pressing or massaging the area immediately after injecting, as this can increase local irritation rather than dispersing the medicine faster.

If lumps keep recurring despite rotating sites and using fresh needles, that pattern is worth raising at your next review. Persistent lipohypertrophy can actually affect how the medicine is absorbed, so it is not purely a cosmetic concern. Your prescriber may recommend a longer rotation cycle, a change of injection site entirely, or a review of injection depth and angle. For a broader look at how Wegovy injections work and how to use the pen, that page covers technique in more detail.

Wegovy is a prescription-only medicine, and the clinical oversight that comes with a regulated service is part of what makes questions like these answerable quickly. If you have concerns about how your treatment is going, or you're thinking about starting and want to understand what the injection experience involves, you can read Wegovy weight loss injections reviews from people who have used the treatment, learn more about Wegovy and how it's used at nume, review Wegovy pricing, or read about weight-loss treatment options more broadly. If you are already a patient and something doesn't feel right, our aftercare team is available seven days a week. When you're ready to speak to a prescriber about starting treatment, a free consultation is the first step.