Short answer: Mounjaro (tirzepatide) is injected under the skin once a week, on the same day each week, in the stomach area, the thigh or the back of the upper arm, using a different spot each time. In the US it comes as a single-dose pen or a single-dose vial, and each pen or vial holds one weekly dose. Follow the Instructions for Use that come with your product.

Key takeaways

  • Mounjaro is injected once a week, at any time of day, with or without meals.
  • It goes under the skin (subcutaneous): the stomach area (at least 2 inches from the belly button), the front of the thigh or the back of the upper arm.
  • US Mounjaro pens are single-dose pens: one pen is one injection, and the needle is built in.
  • If you miss a dose, the prescribing information says to take it within 4 days (96 hours); after that, skip it.
  • Your doctor decides your dose and when it changes; this page only summarizes how the label says to use it.

Mounjaro is a prescription medicine containing tirzepatide, injected once a week. In the US it is approved for adults with type 2 diabetes; the same medicine is sold as Zepbound for weight management. At the pharmacy you may get it as a single-dose pen or as single-dose vials. The basic rules are the same for both; what differs is how the dose is given.

This page is for general information only and is not medical advice. Do your first injection the way your doctor, nurse or pharmacist showed you, and follow the Instructions for Use in the carton.

When and how often do you inject Mounjaro?

Once a week, on the same day every week. The time of day is up to you, and it does not matter whether you have eaten. Picking a fixed day that is easy to remember is the simplest way to avoid missing a dose.

If you need to change your injection day, the prescribing information says there must be at least 3 days (72 hours) between two doses. For more on choosing and changing your day, see which day should you take your GLP-1 injection.

Where do you inject it?

Mounjaro goes under the skin. It is not injected into a muscle or a vein.

  • Stomach area: at least 2 inches away from the belly button.
  • Thigh: the front.
  • Upper arm: the back; someone else usually gives the injection here.

You can keep using the same body area, but choose a different spot each week. Do not inject into skin that is red, hard, bruised or broken. Why rotating matters is covered in GLP-1 injection sites and rotation.

If you use the single-dose pen

The US Mounjaro pen holds one weekly dose, with a hidden needle already attached. You do not attach a needle or set a dose. The general flow looks like this:

  • Wash your hands and check the label: right medicine, right dose, not expired.
  • Look at the medicine: it should be clear and colorless to slightly yellow. Do not use it if it is cloudy, has particles or has been frozen.
  • Pull off the base cap only when you are ready to inject.
  • Place the pen flat against the skin, unlock it and press and hold the button. The Instructions for Use describe two clicks: one when the injection starts and one when it is finished.
  • Keep holding until the injection is complete, as your instructions describe, then lift the pen away.
  • Put the whole used pen in a sharps disposal container.

Always follow the Instructions for Use for your own pen. For general pen tips and common mistakes, see how to use a GLP-1 pen.

If you use a vial

Each Mounjaro vial is single-dose: the whole amount in one vial is one weekly injection. A carton that says four vials holds four weeks of doses.

  • Check that the dose on the vial label matches your prescription.
  • Check that the liquid is clear.
  • Use a new, sterile syringe and needle for every injection; never reuse a vial or a syringe.
  • Draw up and inject the dose exactly the way your doctor or pharmacist showed you.

Syringe markings differ between syringe types. Your pharmacist or doctor should show you which syringe to use and how to draw up the dose; do not work out units on your own.

What if I miss a dose?

According to the prescribing 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 make up for a missed one.

Storage

Keep unused pens and vials in the refrigerator at 36°F to 46°F (2°C to 8°C) and do not freeze them. How long they can stay out of the refrigerator is covered in how to store GLP-1 injection pens.

Keeping track of your injections

After a few weeks it gets hard to remember which day you injected, which dose you took and where. Haftra logs each injection with the day, dose and site, shows you which site is next and reminds you on your dose 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 prescribing information leaves the time up to you, with or without food. What matters is keeping the same day each week.

Is one Mounjaro pen one dose?

Yes, in the US. The Mounjaro pen is a single-dose pen: it gives one weekly injection and is then thrown away in a sharps container. Single-dose vials work the same way: the whole vial is one dose.

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 go back to your usual day. Do not take two doses at once.

Where do you inject Mounjaro?

Under the skin of the stomach area (at least 2 inches 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 prescribing information.

Sources

  • FDA - Mounjaro (tirzepatide) prescribing information and Instructions for Use
  • FDA - Zepbound (tirzepatide) prescribing information
  • U.S. Food and Drug Administration (FDA)

Last reviewed: September 26, 2026