How to Take the Mounjaro Injection: A Practical Step-by-Step Guide

Step 1, Get everything ready before you uncap the pen

Start at least 30 minutes before you plan to inject. Take your pen out of the fridge and let it sit at room temperature, a cold pen is more likely to sting. While it warms up, wash your hands thoroughly with soap and water. Choose your injection site: the outer thigh, the abdomen (keeping a couple of inches away from the navel), or the upper arm. Wherever you injected last week, pick somewhere different this time. Rotating sites reduces the risk of localised skin reactions building up.

Before you do anything else, check the pen window. The liquid inside should be clear or slightly yellow, with no visible particles. If it looks cloudy or you see floating matter, do not use it, contact your prescriber or pharmacist. That quick ten-second window check is worth making a habit of every single week. You'll also want a sterile alcohol swab to clean the skin, and a suitable container ready for the used pen afterwards.

If you're still getting comfortable with the full process, the detailed Mounjaro KwikPen usage guide covers the mechanics of the pen itself in more depth.

Step 2 (Prepare the skin and attach a fresh needle

Wipe the chosen skin area with an alcohol swab and let it air-dry fully) injecting through wet skin can sting more. Do not rub the area dry; let it evaporate on its own, which takes about 20 seconds.

Now attach a new needle to the pen. Peel the foil from a compatible fresh needle, thread it onto the pen tip and turn clockwise until secure. Remove the outer needle cap and set it aside, you'll need it after the injection to recap safely before disposal. Remove the inner needle cap and discard it.

Each injection must use a fresh needle. Reusing needles blunts the tip and increases the chance of skin irritation or blocked delivery. The pen itself is used once weekly across its four-dose lifespan; the needle is single-use every time.

Thinking about when in the week to inject? The guidance on the best time to take Mounjaro explains how to pick a consistent day and time that fits your routine.

Step 3, Inject and complete the dose

Hold the pen like a marker pen, perpendicular to the skin. Press the base firmly and flatly against the site, do not pinch the skin unless your prescriber has advised it. Press the green injection button with your thumb. Keep steady pressure on the skin throughout.

You'll hear a click as the injection starts. Hold the pen firmly in place until a second click confirms the dose is done, then keep it pressed for a further five seconds before lifting. The window will show that the plunger has moved; a partially moved plunger means you may not have received a full dose, so check the leaflet instructions and contact your pharmacist.

Do not rub the injection site after removing the pen. Some brief redness or a small raised area is normal and usually fades within minutes. If the site looks unusually inflamed or feels hard over days, mention it at your next clinical review. The broader overview of the Mounjaro injection covers what to expect from your skin over time.

Step 4 (Dispose of the needle safely and store the pen

Recap the used needle using the outer cap you set aside, then remove and dispose of it into a 1-litre sharps bin) never into a household bin. Replace the pen cap and return the pen to the fridge for next week's dose.

Keep a simple note of the date and site each week (a small calendar note on your phone works well). After four weekly injections the pen is empty; the whole pen goes into the sharps bin at that point. Your local council or community pharmacy can advise on sharps collection. More on timing and routine is covered on the page about the best injection day.

One practical note on cost: Mounjaro is a private prescription medicine and pricing varies by dose and provider. The context behind Eli Lilly's 2025 UK price changes is worth reading if you're weighing up your options. At nume, one transparent price covers the clinical consultation, prescription and next-working-day tracked delivery, no separate fees layered on top.

If you have wider questions about how Mounjaro works as a treatment, the full Mounjaro treatment overview covers eligibility, evidence and what to expect during the programme.