Your step-by-step Mounjaro injection guide

Step 1, Prepare: pen, site, and skin

Take your Mounjaro pen from the fridge about ten minutes before you plan to inject. Cold medicine straight from the fridge doesn't cause harm, but letting it sit briefly at room temperature tends to make the injection more comfortable. Check the pen window: the liquid should be clear or very slightly yellow, with no visible particles. If it's cloudy or discoloured, don't use it, contact your prescriber or our team via the support page.

Pick your site, abdomen (at least 5 cm from the navel), outer thigh, or upper arm. If you're choosing the upper arm and injecting alone, the outer thigh or abdomen is more practical. Keep a rough mental record of where you injected last week; moving around the same site even slightly (a couple of centimetres) each time prevents the small lumps that can build up with repeated injections in exactly the same spot.

Clean the chosen area with an alcohol swab and let it dry fully before proceeding, injecting through wet skin can sting. Pre-saturated alcohol swabs are the easiest option if you don't already have them.

Step 2, Inject: what actually happens when you press the button

Remove the pen cap and the needle cover immediately before use. Press the pen flat against the cleaned skin, firm contact, not a pinch unless your prescriber or the leaflet has advised otherwise. Press and hold the button until you hear or feel two clicks: the first signals the injection has started, the second that it's complete. Keep the pen in place for a few seconds after the second click before lifting it away; this gives the full dose time to deliver.

The detailed technique page covers the two-click sequence with more step-by-step specificity. Most people find the needle itself surprisingly comfortable, tirzepatide's needle is fine-gauge and short. A small amount of bleeding or redness at the site is normal and settles quickly. Do not rub the area afterwards.

The whole process, once you've done it a couple of times, takes under a minute. Many people settle into doing it on the same day each week, some pick a Monday to align with ordering, others a weekend when they're not in a rush.

Step 3 (Dispose and record: the habits that keep you safe

The used pen and needle must go into a sharps container immediately after use) not into the household bin, not into a recycling box. NHS sharps disposal services or community pharmacies can accept full containers; check your local council's guidance for the collection route in your area. Never recap or try to re-use a pen.

Keep a simple note of the date and the site each time you inject. It takes five seconds and it matters: if you're ever unsure whether you injected this week (it happens), your log answers the question without guesswork. It also gives your prescriber useful information at review. For a full overview of what Mounjaro injection pens look like and how the device works, the pen format page covers the KwikPen in more detail.

Information on how to rotate sites correctly and the evidence behind site choice is on the injection site guide. The NHS's tirzepatide patient information at nhs.uk/medicines/tirzepatide is also worth bookmarking for quick reference.

Side effects to watch for after injecting

Nausea is the most common reaction, most noticeable in the first week or two at a new dose. It usually eases as the body adjusts. Other GI effects (loose stools, constipation, burping, reflux) follow a similar pattern: front-loaded, then fading. Eating smaller meals and staying well hydrated helps most people through the early weeks. A full breakdown of what to expect is on the symptoms page.

Seek medical attention promptly for: severe or persistent stomach pain that spreads to the back (this should be assessed urgently, pancreatitis, though uncommon, is a known risk with GLP-1 medicines and was the subject of a 2026 MHRA Drug Safety Update); signs of a serious allergic reaction such as facial swelling, difficulty breathing, or a spreading rash; or significant dehydration from vomiting or diarrhoea that doesn't settle.

You can report any suspected side effect directly to the MHRA via the Yellow Card scheme. For questions about your specific dose or whether a symptom is related to your treatment, our prescribers are available seven days a week through the FAQs or the aftercare line. A question about how much Mounjaro costs privately is answered on the price page, if that's relevant to where you are in the process.

If you'd like to start treatment and haven't yet had a consultation, you can check your eligibility today, it's free, and a GPhC-registered prescriber reviews every application the same day.