Bruising at the Wegovy Injection Site: What the Evidence Says

What the clinical evidence tells us about injection-site bruising

The STEP 1 trial, published in the New England Journal of Medicine, enrolled over 1,900 adults using once-weekly subcutaneous semaglutide 2.4 mg, and injection-site reactions were among the most commonly tracked local events across the STEP programme. The NHS medicines page for semaglutide lists injection-site reactions (bruising, pain, redness, swelling and itching) under side effects that affect up to 1 in 10 people. Bruising sits in that category rather than a rarer one, which means if your arm or abdomen turns purple after a dose, you are far from alone.

The mechanism is straightforward: subcutaneous tissue is richly supplied with tiny capillaries. A pre-filled pen like Wegovy delivers medicine just below the dermis, and even a perfect injection can nick one of those vessels. The result is a small haematoma (what most people simply call a bruise) as blood disperses under the skin. It is not a sign that the medicine has gone to the wrong place, and it does not affect how well the dose is absorbed.

Bruising is more likely in the first weeks of treatment, when the technique is still new, and may settle as users become more confident. People who take anticoagulants or antiplatelet medicines, or who bruise easily in everyday life, may notice it more frequently, worth mentioning to your prescriber if it becomes a pattern. Our guide to bruising from a Wegovy injection covers what typically causes it and how to manage it if it becomes a recurring concern.

Why technique has a bigger effect than most people expect

Even small adjustments in how you inject can meaningfully reduce bruising. The NHS England guidance on weight-management injections and Wegovy's own Patient Information Leaflet both emphasise site rotation and correct subcutaneous depth. A few practical points the evidence supports:

Temperature: injecting a pen taken straight from the fridge is more likely to sting and cause local trauma. Letting it sit at room temperature for roughly 30 minutes before use (check the exact storage window in your leaflet, as the manufacturer's guidance is the authoritative source) makes the injection more comfortable and may reduce bruising.

Needle condition and pen priming: each Wegovy pen is single-use and pre-primed; following the steps in the Patient Information Leaflet keeps the injection smooth. If you use separate needle tips, ensure you are using a fresh one each time, a blunted needle drags more tissue and increases bruising risk. Replacement needles are available from our pharmacy if needed.

Skin pinch and angle: a gentle two-finger pinch lifts subcutaneous tissue away from the muscle, reducing the chance of hitting a blood vessel. The recommended injection angle for subcutaneous pens is typically 90 degrees into pinched skin, your Patient Information Leaflet gives the exact technique.

Pressure, not rubbing: holding gentle pressure over the site for ten seconds after withdrawal helps, but rubbing the spot can spread blood under the skin and enlarge the bruise.

Rotating sites is probably the single most effective habit. Injecting the same spot repeatedly causes localised trauma to vessels that have not fully recovered. Mapping out a rotation across abdomen zones, both outer thighs and each upper arm gives tissue time to heal between doses.

Bruise at a Wegovy injection site: what is normal and what is not

Most injection-site bruises are small (thumbnail-sized or less), appear within hours, peak in colour by day two or three and fade over five to ten days. The skin may feel slightly tender to touch. That is the expected trajectory and needs no treatment beyond patience.

It is worth getting medical advice (contact your GP, call 111, or speak to our prescriber team via our support line) if any of the following apply:

The bruise keeps expanding beyond 48 hours. There is a firm, raised lump that does not soften. The area becomes hot, increasingly red, or you develop a fever. You notice bruising appearing in areas away from the injection site as well, which could point to a systemic issue unrelated to the injection. You are on blood-thinning medication and the bruise is large or painful.

Those situations are uncommon. The reality is that most people message their prescriber, are reassured within the day, and carry on with treatment. But prescribers exist precisely to make that call, not to leave you guessing.

Reducing bruising over time: a few more practical notes

Many users find bruising drops off significantly after the first month as their confidence with the pen grows. Staying well hydrated keeps subcutaneous tissue in better condition. Avoiding injecting into areas with visible surface veins or broken skin is sensible. Alcohol swabs are fine to use for site cleaning, pat the area dry and let it air for a few seconds before injecting so that residual alcohol does not cause additional stinging. Clean swabs are available from our pharmacy if you need a reliable supply.

Bruising after dose increases can tick up briefly too, simply because a higher-volume dose requires a slightly longer contact time with the tissue. It usually settles again within a week or two. If you are noticing bruising after every injection regardless of site or technique, that pattern is worth raising at your next clinical review rather than trying to troubleshoot alone.

You can read more about choosing and rotating your sites on our upper arm injection guidance page, or explore the broader picture of weight management treatment to see how Wegovy fits alongside lifestyle changes. Anyone thinking about starting treatment through a regulated pathway can read about the full clinical process on our about us page. For a broader look at the treatment itself, our Wegovy overview covers eligibility, results evidence and how the prescription process works. If you have questions our FAQs page does not cover, our prescribers are available seven days a week through the FAQs section or direct contact.

Wegovy is a prescription medicine. If you are considering starting or continuing treatment, start a free consultation with our GPhC-registered prescribers, a real clinician reviews your information the same day.