How to Use the Tirzepatide Pen Correctly

Your pen is in the fridge, here's what to do before you inject

Picture Sunday evening: you've decided that once a week works best for you, your pen has been sitting in the fridge since it arrived, and you're about to do this for the first time. Start by taking the pen out and letting it sit at room temperature for a short while before you use it, injecting a cold solution is more likely to sting. While it's warming up, wash your hands thoroughly with soap and water.

Check the pen window before you begin. The liquid inside should be clear and colourless or very slightly yellow; if it looks cloudy, contains particles or has changed colour, don't use it and contact your prescriber. Remove the base cap (the grey end) and attach a new needle by peeling the paper seal, pushing the needle straight onto the pen and turning clockwise until it's snug. Pull off the outer needle cap and then the inner one, and you're almost ready. Our step-by-step injection guide covers this preparation sequence in more detail if you want a more visual walkthrough.

Clean the skin at your chosen site with an alcohol swab and let it dry completely, injecting through wet skin can cause brief stinging. Pinch a fold of skin gently if you're using the abdomen or thigh; you don't need to pinch for the upper arm if someone else is helping you.

The injection itself, what the pen does and what you'll feel

Press the pen flat against your skin at a 90-degree angle. Push the purple injection button firmly and hold it down. You'll hear and feel a click when the injection starts, and a second click shortly after when it's finishing. Keep the pen held against your skin for about ten seconds after that second click, this ensures the full dose is delivered. Lift the pen away, and the needle guard will spring forward automatically to cover the needle tip.

Some people feel very little; others notice a mild pressure or brief sting. A small red mark or slight bruising at the site is common and usually fades within a day or two. Don't rub the skin after injecting, it doesn't help the medicine absorb and may increase bruising. If you're uncertain about any part of this technique, our guide on how to take tirzepatide covers common points of confusion, and our prescribers are available for aftercare questions seven days a week.

The NHS patient information for tirzepatide, available at nhs.uk/medicines/tirzepatide, also outlines the injection procedure in plain language alongside important safety information.

Rotating sites and disposing of needles safely

Where you inject matters more than most people realise. The three licensed sites (abdomen, front or outer thigh, and upper arm) each have a good layer of subcutaneous fat and are accessible for most people. Staying in exactly the same spot week after week can cause lipohypertrophy: a hardening under the skin that slows medicine absorption and can affect how well treatment works. A simple rule is to move at least a few centimetres from last week's spot, and to rotate between the three sites over time.

Never inject into skin that is bruised, scarred, tender or affected by a rash. Avoid the area directly around the navel for abdominal injections.

Once the injection is done, carefully replace only the outer cap on the needle (not the inner one) and unscrew the needle from the pen. Drop used needles straight into a sharps container; they should never go into your household bin. Put the base cap back on the pen and return it to the fridge. Your local council or GP surgery can advise on sharps collection in your area.

If you're wondering about the cost of ongoing treatment, our Mounjaro pricing page explains what's included in a private prescription from a regulated UK pharmacy.

What to do if something doesn't go to plan

Missed a dose? Check your Patient Information Leaflet, the rule depends on how close you are to your next scheduled injection, and your prescriber is the right person to advise on your specific situation. Don't double up without guidance.

If after injecting you notice no click, or you're not sure the full dose was delivered, don't inject again to compensate. Make a note and speak to your prescriber or contact our aftercare team before your next dose. They've heard this question more than a few times.

Seek urgent medical help if you develop severe stomach pain that spreads to your back, with or without vomiting, this can be a sign of pancreatitis, which the MHRA has identified as an infrequent but serious side effect of GLP-1 medicines in its Drug Safety Update guidance, available via the Yellow Card scheme. Other side effects, including nausea and fatigue, are more common and generally settle within a couple of weeks as your body adjusts.

If you're new to Mounjaro or considering starting treatment, you can learn more about the medicine and whether it may be suitable for you, including details about the tirzepatide pens used to administer it, or speak to our prescribers through a free consultation on our treatment page.