If you've never self-injected before, the idea can feel daunting. But Mounjaro uses a pre-filled pen that makes the process straightforward — the dose is pre-measured, the needle is built in, and the whole injection takes a few seconds. Here's how to do it.
Before your first injection
Your prescriber or pharmacist should demonstrate the injection technique before your first dose. If they don't offer this, ask. The Mounjaro pen also comes with a detailed patient information leaflet with illustrated instructions.1
Step-by-step
1. Choose your injection site
Mounjaro can be injected into three areas:
- Abdomen (stomach area) — at least 5cm away from the belly button. This is the most common site
- Front of the thigh — the middle outer area
- Upper arm — the back of the arm (this is easier if someone else is injecting for you)
Rotate your injection site each week — don't inject in the same spot every time, as this can cause skin irritation or lumps.
2. Prepare
- Wash your hands
- Check the pen — make sure the medication is clear and colourless (don't use it if it's cloudy, discoloured, or contains particles)
- Check the expiry date
- If the pen has been in the fridge, you can let it warm to room temperature for a few minutes (this may reduce discomfort), but it's fine to inject straight from the fridge
- Clean the injection site with an alcohol swab if provided, or clean skin
3. Inject
- Remove the pen cap
- Place the base of the pen flat against your skin at the injection site
- Unlock the pen and press the injection button. You'll hear a click when the injection starts
- Hold the pen against your skin until you hear a second click and the grey plunger is visible — this confirms the full dose has been delivered (takes about 5–10 seconds)
- Remove the pen from your skin
4. After injection
- Don't rub the injection site
- You may see a small drop of blood or medication at the site — this is normal
- Replace the pen cap and store the pen according to the storage instructions
- Dispose of the pen in a sharps bin when all 4 doses have been used (each pen contains 4 weekly doses)
Storage
- Unopened pens: Store in the fridge (2–8°C). Do not freeze
- Opened (in-use) pens: Can be stored at room temperature (up to 30°C) for up to 21 days. After 21 days, discard even if doses remain
- Keep out of direct sunlight and away from heat sources
Missed dose
If you miss a dose and it's been less than 4 days (96 hours) since the missed dose was due, inject as soon as you remember and then continue your regular weekly schedule.
If it's been more than 4 days, skip the missed dose and inject on your next regularly scheduled day. Do not inject a double dose to make up for a missed one.1
Tips for reducing discomfort
- Let the pen reach room temperature before injecting
- Pinch the skin gently at the injection site (especially if you're lean)
- Inject slowly and steadily — don't rush
- Rotate sites each week
- Relax the muscle at the injection site
Most people describe the injection as no more than a slight pinch. The needle is very small and the process becomes routine quickly.
Note: Wegovy pens work similarly
If you're using Wegovy rather than Mounjaro, the injection process is very similar — same sites, same technique. The main difference is the pen design (Wegovy uses a FlexTouch pen). Always follow the specific instructions in your medication's patient information leaflet.