Mounjaro Injection Sites: Where to Inject for Best Results

If you’re new to weight loss injections or have recently switched to Mounjaro, it’s important to understand the recommended injection sites and how to administer your medication safely.

In this blog post we’ll cover injection and storage instructions for your weight loss treatment, as well as the best places to inject Mounjaro for optimum results.

Article summary:

• Mounjaro is the brand name for a weight loss treatment containing the active ingredient tirzepatide, which is injected into your chosen injection site once a week using a pre-filled pen.
• The treatment should be injected into the fatty tissue of the back of your upper arm, your stomach or thigh.
• You can inject into the same area of your body each week, but it’s best to choose a slightly different spot to reduce the risk of irritation. Your choice of injection site doesn’t impact the effectiveness of the medication.

Mounjaro injection sites

Mounjaro is an MHRA-approved prescription weight loss injection that contains the active ingredient tirzepatide. [1]

To administer it, once a week you’ll self-inject using the pre-filled pen into your chosen “injection site”.

Why correct injection is important

Dr. Sophie Dix, our Head of Medical Affairs, explains: “Like any medication, Mounjaro needs to be taken correctly in order for it to be effective. That’s why it’s important to follow the injection instructions carefully, to make sure you receive your full dose each time for best results.”

Best injection sites for Mounjaro

The recommended injection sites for Mounjaro are the back of your upper arm, your stomach, or the front of your thigh. Choose whichever area you feel most comfortable with, and make sure you can see the dose window on your pen when you’re injecting. [2] This will help you see that the injection is being administered correctly.

Injecting into your thigh

• Where exactly to inject: Inject into the fatty area on the front or outer part of the upper thigh, between the hip and knee.
• Our tips: If it feels easier, you can pinch your skin slightly to help you to inject.

Injecting into your stomach

• Where exactly to inject: Inject into your lower stomach, staying at least 5cm from your belly button.
• Our tips: You may find it easier to sit down while you administer the injection.

Injecting into your upper arm

• Where exactly to inject: Inject into the fatty area on the back of your upper arm.
• Our tips: Ask someone to inject your medication for you if you’re choosing this area, as it may be difficult to reach and to see the dose window.

Continue reading below for step-by-step instructions on how to inject Mounjaro into your chosen injection site.

Warning: Do not inject into skin that is bruised, sore, red, hard, scaly, scarred, damaged or lumpy.

Does the injection site impact side effects?

No, your choice of injection site won’t impact the Mounjaro side effects you experience. When Mounjaro is injected correctly under your skin, the exposure to the active ingredient tirzepatide, the results and side effects are similar across all injection sites. [3]

How to inject Mounjaro safely

Mounjaro is taken as a once-weekly injection, and is administered using an injection pen. Mounjaro KwikPen is a disposable, multi-dose pre-filled pen for single patient use (you should never share it). The pen contains 4 fixed doses, with 1 dose taken each week. [3]

When you receive your Mounjaro medication, the Patient Information Leaflet inside the box will provide detailed instructions on how to administer your injection, including which injections sites to use. You’ll also receive a free sharps container with your first order. You can get in touch with your clinical team here at MedExpress if you have any questions or concerns.

You’ll take your Mounjaro medication on the same day each week, and while you can take it at any time of the day, we recommend trying to choose the same time each week to create a routine that makes your medication easier to remember. If that day is no longer convenient for you to administer your medication, it is possible to switch your day. Just make sure there are at least 3 days (72 hours) between your last dose and your next (new weekly) one. [3]

Preparing for your Mounjaro injection

Before administering your medication, you’ll need to get the injection pen ready. First, remove it from the refrigerator, leaving the cap on until you’re ready to inject. Next, read the label to check the dose and expiration date to ensure that it’s correct and in date. Then check the pen to make sure it’s not damaged and the solution is not frozen or cloudy. [4]

When you’re ready to inject, you’ll need to select a new needle and check it to ensure it's not damaged. You’ll need to do this each time you administer your medication. If you see any damage, dispose of the needle in a sharps bin. Do not use a damaged needle as it may not be fully sterile and safe to use.

Then, you need to push the needle onto the pen and twist until it's secure. Remove both caps, disposing of the inner cap and keeping the outer one for later to safely dispose of your medication.

Priming the pen

This is an important step. Priming removes air from the cartridge and makes sure that your pen is working correctly. Your pen has been primed if a small amount of medicine comes out of the tip of the pen needle. Here are your step-by-step instructions for how to prime your pen:

1. Slowly turn the dose knob, until you hear 2 clicks and the extended line is shown in the dose window.
2. With the needle pointing upwards, tap the cartridge holder gently to collect air bubbles at the top.
3. Release some medicine into the air by pushing the dose knob in until it stops.
4. Slowly count to 5 while holding the dose knob. This will expel a small amount of medicine, but don’t worry, it won’t affect your dose.

Choosing the injection spot

Your medication must be delivered via subcutaneous injection, which means it goes into the fatty tissue just under your skin. Never inject into a muscle or a vein. You should also try to avoid areas of scarring, bruising, stretch marks, rashes or broken skin.

As mentioned above, you can choose to inject it in your stomach, thigh or the back of your upper arm. The area you pick is known as your ‘injection site’. Just remember to clean the area with the alcohol swab provided before you inject. [4]

So long as you inject your medication as directed into one of these three injection sites, it doesn’t matter which one you choose. Some people find their abdominal area is the easiest to access for full visibility, or you might like to use your upper arm if someone is injecting it for you. The best Mounjaro injection site is the one you’re most comfortable with.

Administering the injection correctly

You may feel worried by the idea of injecting for the first time, but don’t worry. It’ll soon become part of your weekly routine. Here’s how to inject your treatment correctly, step by step:

1. Wash your hands with soap and water.
2. Clean your chosen injection site with the alcohol wipes provided.
3. Turn the dose knob until it stops and the ‘1’ icon is shown in the dose window.
4. Position the pen at the injection site at a 90-degree angle.
5. Insert the needle into your skin, and inject the medication by pressing and holding the dose button until ‘0’ appears. Continue holding for 5 seconds to ensure full delivery.
6. Remove the needle from your skin.
7. If blood appears at the injection site, press on it lightly with a clean tissue, but do not rub the area.

Disposing of your injection pen after

Injections and injection pens must be disposed of safely. We’ll send you a sharps container with your first Mounjaro order to put your used injection pens in. Make sure you keep your container out of the reach of children.

When you’re ready to dispose of it, don’t put any element in your household recycling. When your sharps bin is full you can take it to your local pharmacy to be disposed of, or it may be able to be collected by your local council.

Post-injection care

Want to be sure you administered your dose correctly? After every injection, check:

• The dose counter has returned to ‘0’ in the window of the pen.
• You held the pen against your skin for 5 seconds.
• The plunger has moved down inside the pen.

If all of these have happened, your dose has been delivered and you don’t need to do anything else.

Injection site rotation

Each week, inject into a different spot to help prevent injection site reactions. You can use the same body part every week if you prefer, but avoid injecting right next to the previous week’s dose, to help minimise skin irritation. [5]

How to inject Mounjaro: FAQs

Where should I inject Mounjaro for best results?

In clinical trials, tirzepatide has been shown to help people experience weight loss of 22.5% after 72 weeks of treatment. [6] However, all weight loss medications must be prescribed alongside recommended lifestyle changes, such as a reduced calorie diet and increased exercise, to achieve lasting results. [7]

Why does the injection hurt?

If your injection hurts or feels painful, it may be because the needle has passed through a sensitive area of skin, the injection site is irritated, or it's been injected into tissue that is bruised or already inflamed.

Mild, short-lived pain or tenderness is common as part of an injection site reaction. If the pain is severe, persists or worsens, or is accompanied by spreading redness, swelling, pus or fever, contact your healthcare professional or seek immediate medical help. [8]

Is it normal that my injection site is swollen or red?

Some redness or mild swelling, itching or tenderness is common and may be a local injection site reaction to Mounjaro. Don't rub the area, and use a different spot for your next dose. Keep an eye on any irritation to make sure it improves, and contact our clinical team if you need more support.

Do I need to pinch my stomach when injecting Mounjar?

No, you shouldn't need to pinch the skin on your stomach to inject Mounjaro. Firmly place the pen's base flat against your skin and follow the instructions carefully to deliver your dose.

How often should I rotate my injection site?

Rotate your injection site every week. That doesn’t mean you have to use a different body area each time, but you should always choose a slightly different spot to help reduce the risk of irritation and injection site reactions. [8]

What should I do if I miss a dose?

There might be a time when missing your usual injection day is unavoidable. If this happens, just take the missed dose as soon as possible within 4 days (96 hours). If it has been more than 4 days since the missed dose, skip that one entirely and take your next dose on the next regularly scheduled day.

Thinking of starting weight loss treatment? At MedExpress, we offer online consultations with regular clinical check-ins, and a range of weight loss treatments including Mounjaro, Wegovy Pen, Wegovy Pill and Foundayo and our team can help you find the right treatment for you.

References

1. MHRA. MHRA authorises diabetes drug Mounjaro (tirzepatide) for weight management and weight loss [Internet]. GOV.UK. 2023 [cited 2026 Oct 1]. Available from: https://www.gov.uk/government/news/mhra-authorises-diabetes-drug-mounjaro-tirzepatide-for-weight-management-and-weight-loss
2. Instructions for use Mounjaro® 15 mg KwikPen® solution for injection in pre-filled pen
3. tirzepatide [Internet]. [cited 2026 Oct 1]. Available from: https://www.medicines.org.uk/emc/files/usermanual.15481.pdf
4. Mounjaro KwikPen Package Leaflet: Information for the Patient [Internet]. 2026 [cited 2026 Oct 1]. Available from: https://www.medicines.org.uk/emc/files/pil.15485.pdf
5. How to Use, Dosing & Side Effects | Mounjaro® (tirzepatide) [Internet]. mounjaro.lilly.com. Available from: https://mounjaro.lilly.com/how-to-use-mounjaro#how-to-use
6. Hirsch LJ, Strauss KW. The Injection Technique Factor: What You Don’t Know or Teach Can Make a Difference. Clinical Diabetes : A Publication of the American Diabetes Association [Internet]. 2019 July 1 [cited 2026 Oct 2];37(3):227–33. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6640874/
7. Jastreboff AM, Aronne LJ, Ahmad NN, Wharton S, Connery L, Alves B, et al. Tirzepatide Once Weekly for the Treatment of Obesity. New England Journal of Medicine [Internet]. 2022 June 4 [cited 2026 Oct 1];387(3):205–16. Available from: https://www.nejm.org/doi/full/10.1056/NEJMoa2206038
8. National Institute for Health and Care Excellence. Medicines and surgery | Overweight and obesity management | Guidance | NICE [Internet]. Nice.org.uk. NICE; 2025 [cited 2026 Oct 1]. Available from: https://www.nice.org.uk/guidance/ng246/chapter/Medicines-and-surgery
9. Mounjaro KwikPen 10mg solution for injection in pre-filled pen [Internet]. Medicines.org.uk. 2025 [cited 2026 Oct 1]. Available from: https://www.medicines.org.uk/emc/product/15484/smpc