Short answer: Mounjaro (tirzepatide) is injected under the skin once a week, on the same day each week, into the tummy, the thigh or the back of the upper arm, using a different spot each time. In the UK it comes as the KwikPen, which holds several weekly doses. The instructions for use in your pack set out each step.

Key takeaways

  • Mounjaro is injected once a week, at any time of day, with or without food.
  • It goes under the skin (subcutaneous): the tummy (about 5 cm from the belly button), the front of the thigh or the back of the upper arm.
  • The KwikPen holds several weekly doses; you attach a new needle for every injection.
  • If you miss a dose, the product information says to take it within 4 days (96 hours); after that, skip it.
  • Your GP or prescriber decides your dose and when it goes up.

Mounjaro is a prescription-only medicine containing tirzepatide, taken as a once-weekly jab. In the UK it is licensed for type 2 diabetes and for weight management, and it comes as the KwikPen: one pen from which you take a weekly dose over several weeks.

This page is for general information only and does not replace medical advice. Do your first injection the way your nurse, pharmacist or prescriber showed you, and follow the instructions for use in the pack.

When do you inject Mounjaro?

Once a week, on the same day every week. The time is up to you, before or after a meal. A fixed day that is easy to remember is the simplest way not to miss a dose.

If you need to change your injection day, the product information says there should be at least 3 days (72 hours) between two doses. For more, see which day should you have your weight-loss injection.

Where do you inject it?

Mounjaro goes under the skin, not into a muscle or a vein.

  • Tummy: about 5 cm away from the belly button.
  • Thigh: the front.
  • Upper arm: the back; someone else usually injects here.

You can keep using the same area, but choose a different spot each week. Do not inject into skin that is red, hard, bruised or broken. Why rotating matters is explained in weight-loss injection sites and rotation.

The KwikPen at a glance

The exact steps are in the instructions for use for your pen. In outline:

  • Wash your hands and check the label: right medicine, right dose, in date.
  • Check the liquid is clear and colourless to slightly yellow; do not use it if it is cloudy, has particles or has been frozen.
  • Attach a new needle for every injection and carry out the preparation steps described in the instructions for use.
  • Place the pen straight against the skin, press the button and hold for as long as the instructions say.
  • Take the needle off and put it in a sharps bin; do not store the pen with a needle attached.

Taking a different amount from the pen than the dose printed on it, for example by counting clicks, is not a use described in the product information. For general pen and needle tips, see how do you use a weight-loss injection pen.

What if I miss a dose?

According to the product information:

  • If 4 days (96 hours) or less have passed since the missed dose, take it as soon as you remember, then take the next dose on your usual day.
  • If more than 4 days have passed, skip the missed dose and take the next one on your usual day.
  • Never take two doses at the same time or close together to catch up.

Storage

Keep unused pens in the fridge at 2°C to 8°C and do not freeze them. How long a pen can be kept at room temperature is covered in how should weight-loss injections be stored.

Keeping track of your injections

Which day, which dose, which spot: after a few weeks that is hard to keep in your head, especially when one pen holds several doses. Haftra logs each injection with the day, dose and site, counts the doses left in your pen and reminds you on your injection day. It does not suggest doses; it only follows your plan. It is free.

iPhone, iPad and Apple Watch. Free.

Frequently asked questions

What time of day should I inject Mounjaro?

The product information leaves the time up to you, with or without food. What matters is keeping the same day each week.

How many doses are in a Mounjaro KwikPen?

The KwikPen holds several weekly doses of the same strength. The exact number is printed on the pack and in the instructions for use.

What happens if I miss a Mounjaro dose?

If 4 days (96 hours) or less have passed, take it as soon as you remember. If more time has passed, skip it and carry on from your usual day. Never take two doses at once.

Where do you inject Mounjaro?

Under the skin of the tummy (about 5 cm from the belly button), the front of the thigh or the back of the upper arm, using a different spot each week.

Can I change my Mounjaro injection day?

Yes, as long as there are at least 3 days (72 hours) between two doses, according to the product information.

Sources

  • EMA: Mounjaro (tirzepatide), summary of product characteristics and package leaflet
  • MHRA (Medicines and Healthcare products Regulatory Agency)
  • NHS: Obesity treatment

Last reviewed: 26 September 2026