Where do you inject Mounjaro — and how do you do it correctly?

Step 1, Pick one of the three approved injection sites

The Mounjaro KwikPen is designed for subcutaneous use, meaning the medicine goes into the fatty tissue just beneath the skin rather than into muscle. The three sites licensed in the SmPC are the abdomen, the front or outer thigh, and the outer upper arm. All three work; none is clinically superior for most people, though some find the abdomen most convenient for self-injection.

Abdomen: aim at least five centimetres away from your navel. The lateral (side) areas of the stomach tend to have more subcutaneous fat and are generally easier to reach. Thigh: the front and outer surface, roughly halfway between the knee and the hip, is the target, avoid the inner thigh entirely. Upper arm: the fleshy outer area works well, though some people find this site harder to manage without help, so it is often more practical when someone else is injecting. If you are unsure about the practicalities of each location, our guide to where you can inject the Mounjaro pen explains the options clearly, and our guide to where to inject Mounjaro covers positioning in more detail.

A question our prescribers hear most weeks: "Can I inject through clothing?" The short answer from the SmPC is no, the skin should be exposed and clean.

Step 2, Prepare the pen and your skin

Take the pen out of the fridge and let it reach room temperature for around 30 minutes before injecting; cold medicine can sting more and slow the KwikPen's mechanism. Check the liquid through the window, it should be clear or very slightly yellow with no visible particles. If it looks cloudy or discoloured, do not use it.

Clean the chosen site with an alcohol swab and allow it to dry fully before injecting. Injecting into wet or damp skin can carry surface bacteria into the tissue. Sterile alcohol swabs designed for this purpose are the right tool; cotton wool and household antiseptic are not recommended.

Remove the pen cap, press the pen flat against the skin (no need to pinch on the abdomen for most people; a gentle pinch can help on leaner thigh or arm sites), and press the button. Hold the pen in place until the indicator window turns completely red and you hear or feel a second click, this confirms the full dose has delivered. The NHS tirzepatide patient information page has clear step-by-step guidance that walks through the injection process in plain language.

Step 3, Rotate your sites systematically every week

Rotation is not optional. Injecting into exactly the same patch of skin repeatedly causes small areas of hardened fat to build up (lipohypertrophy) which reduces absorption unpredictably and can blunt the medicine's effect. The fix is straightforward: move to a different spot each week, and within any given site, vary the exact point of injection by a few centimetres.

A practical system many people use is a rough clock-face approach on the abdomen, moving one or two positions each week. Others alternate abdomen one week, thigh the next, cycling through sites over three or four weeks. Either works as long as you are consistent. You can find detailed site-by-site guidance for the thigh on our page about injecting Mounjaro in the leg, and similarly for the arm on our page covering upper-arm injection technique.

After injecting, dispose of the pen cap safely. A 1-litre sharps container is the correct disposal route for used Mounjaro pens, your local pharmacy can advise on collection points.

What can go wrong and when to seek help

Mild redness, itching or a small raised area at the injection site is common and usually settles within a day or two. Bruising is more likely if you inject into a blood vessel by accident, it looks alarming but is rarely serious. Avoid injecting into skin that is bruised, scarred, tattooed or affected by a skin condition, as absorption will be inconsistent and irritation more likely.

Contact your prescriber or GP promptly if you notice hard lumps that do not resolve within two weeks, signs of infection (increasing warmth, spreading redness, discharge), or a more generalised reaction such as hives, swelling of the face or throat, or breathing difficulty, the last of these needs urgent emergency attention. For general questions about your injection routine, our guide to finding your best injection site covers individual factors a prescriber weighs up. The Mounjaro SmPC on the Electronic Medicines Compendium remains the definitive reference for storage windows, missed-dose guidance and contraindications, your Patient Information Leaflet reprints the key parts in plain English.

If you are considering Mounjaro and want a prescriber to assess whether it is the right option for you, check your eligibility with a free consultation at nume. Every application is read the same day by a GPhC-registered Independent Prescriber, not software.