A lump after your Wegovy shot — what's normal, what isn't

You've found the lump, here's what's likely happening

Picture the moment: you retract the pen, press the skin for a few seconds as the leaflet says, and notice a pea-sized bump has appeared. It wasn't there before. It might be slightly tender when you press it, and the skin above it looks a touch pink.

This is almost certainly a local injection-site reaction. When a subcutaneous medicine is deposited into the fatty tissue just beneath the skin, the body responds to both the needle and the fluid itself. A small amount of localised swelling, redness or firmness is the immune system doing its ordinary job. The bump you can feel is typically a combination of minor tissue irritation and the medicine dispersing through the subcutaneous layer. These reactions are listed in the Wegovy patient information leaflet as common, and the NHS semaglutide medicines page confirms injection-site reactions as an expected side effect of this medicine class.

For most people, the lump flattens within 24 to 72 hours. Some last up to a week. Tenderness usually fades faster than the visible swelling. If your lump fits this description and is shrinking day by day, you're almost certainly watching a normal process run its course. More detail on what the first day after an injection typically feels like is covered in our guide to what to expect the day after a Wegovy shot.

When a lump means something else, the signs that change the picture

Most lumps are uneventful. A few aren't, and it helps to know which features move a lump from the reassuring category into the call-your-prescriber one.

Lipohypertrophy is the main one to understand. This is a build-up of fatty tissue that develops when the same small patch of skin is injected repeatedly over months. The area becomes rubbery, thickened and noticeably different in texture from surrounding skin. It isn't dangerous in the same way an infection is, but it does matter clinically: medicine absorbed through lipohypertrophic tissue is absorbed erratically, which can affect how well your treatment works. The fix is straightforward, rotate sites more widely and give the affected patch a proper rest, sometimes for several weeks.

Signs that suggest infection (rare, but real) are different in character: increasing heat in the area after the first 24 hours, the lump continuing to grow rather than shrink, fever, spreading redness or pus. An infected injection site needs clinical attention promptly, not watchful waiting.

Haematoma (a pocket of blood under the skin) can also produce a lump, usually bluish or bruised in appearance rather than flesh-coloured. If your lump looks more like bruising than swelling, our page on bruising after a Wegovy shot covers that scenario in full.

A lump that hasn't changed size or improved after two weeks deserves a message to your prescriber rather than another week of hoping. Our contact page has the quickest routes to reach the aftercare team.

Practical steps that actually reduce how often lumps appear

Technique matters more than people realise, and small adjustments make a real difference to whether injection-site reactions become a recurring problem or a rare one.

Site rotation is the single most useful habit. The three licensed sites for semaglutide are the abdomen (at least 5cm from the navel), the front of the thigh, and the outer upper arm. Moving between them weekly, and moving around within each site rather than always returning to exactly the same spot, gives tissue time to recover between doses.

Injecting into cold skin straight from a walk outside, or into skin you've just rubbed vigorously, can worsen local reactions. Letting the pen reach room temperature before injecting helps. So does keeping the pen still and pressed firmly against the skin for the full count after you've released the dose, removing it early can leave medicine tracking back up the needle track rather than dispersing properly.

If you're regularly getting lumps in the upper arm, it's worth reading about arm pain and discomfort after Wegovy injections, site-specific technique tips are covered there. A broader overview of what normal recovery looks like across the week sits on our post-injection guidance page.

One note on storage: the NHS advises that semaglutide pens should be stored in the fridge between 2°C and 8°C, and the patient information leaflet sets out exactly how long a pen can sit at room temperature, always defer to that leaflet for the specific window, since injecting degraded medicine can also increase site reactions.

What to do next, and when to act quickly

For a typical small lump that's already fading: no special action is needed. Keep the area clean, avoid pressing or massaging it (which can push medicine into the wrong tissue layer), and make a note to inject at a different site next time. Most lumps are an inconvenience, not a complication.

If you're unsure which category your lump falls into, the aftercare team at nume is available seven days a week. A prescriber can look at photos, ask the right questions and tell you confidently whether what you're seeing is within the expected range. The MHRA's Yellow Card scheme also exists for reporting any side effect you think is worth flagging officially, including persistent injection-site problems.

For people still deciding whether Wegovy is right for them, our page on how semaglutide works goes deeper into the medicine itself, and the Wegovy overview covers the full picture from eligibility to how treatment is structured. Questions about cost come up often too, the where to buy Wegovy page addresses what legitimate private access looks like and what to watch out for. If you'd like a prescriber to review your specific situation, you can speak to our prescribers via a free consultation and get a same-day clinical review.