Before your first injection
Ask the service supplying your pen for training if the leaflet or demonstrations leave you unsure. Check the medicine name, strength, expiry date and your prescription label. Look at the liquid as the leaflet describes. It should be clear and colourless to slightly yellow, with no visible particles.
You need compatible disposable pen needles and a sharps bin. The UK product information says needles are not included in the medicine pack, though your pharmacy may supply them separately. Check your delivery, since providers do not all include the same extras.
The steps in the instructions
The supplied instructions cover fitting a new needle, priming, setting the dose, injecting, checking the dose is complete and removing the needle safely. Priming is part of using the pen. Do not skip it to save medicine. Follow the exact order and the troubleshooting advice for your pen.
Use the illustrated manual in your pack as your main guide. If your pen or its instructions look different from a video you have watched, ask your pharmacy which applies. Do not follow a US single-dose autoinjector tutorial for a UK KwikPen or improvise your own method.
Where to inject
Inject Mounjaro under the skin of your abdomen or thigh. Another person can inject into the back of your upper arm. Move to a different spot each week. Ask for advice before injecting into skin that is damaged or badly irritated.
If you also use insulin, the product information says to inject at a different site. Never mix the two medicines in one syringe. A diabetes nurse or pharmacist can help you plan sites if you use several injectable treatments.
Each pen gives four doses
The pen is designed to deliver four doses of your prescribed strength. Do not count clicks to make an unofficial extra dose, force the mechanism or draw out leftover liquid with a syringe. Liquid left in the pen is no accurate extra dose, and pen designs and fill details can change.
Never share a pen, even with a new needle. Use a fresh needle for every injection and follow the instructions on removing and storing needles. Leaving a needle on the pen causes avoidable problems with the device and with contamination.
When something goes wrong
If you are unsure a dose went in, do not repeat it straight away. Contact your pharmacist or prescribing team with the pen details and a description of what happened. Keep the pen and packaging in case the pen needs checking for a fault.
A small reaction at the injection site differs from a serious allergy. Get emergency help for difficulty breathing, a swelling throat or collapsing. If the injection area becomes more painful, hot or inflamed, ask a clinician to look at it and do not keep injecting close by. Good training teaches you the normal steps and who to contact when something fails.
Sources
Your own medicine leaflet and prescriber come first. A source from another country does not mean the same rule applies in the UK.
- Mounjaro UK Summary of Product Characteristics, updated September 2026 medicines.org.uk
- Mounjaro UK patient information leaflet medicines.org.uk
- Frimley Health NHS: disposal of sharps waste fhft.nhs.uk
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