Mounjaro (tirzepatide) is a once-weekly subcutaneous injection licensed in the UK for type 2 diabetes mellitus and weight management in adults with obesity or overweight with weight-related comorbidities. Knowing the correct places to give Mounjaro shot is essential for optimal drug absorption, patient comfort, and minimising injection site complications. Three approved sites—abdomen, thigh, and upper arm—provide safe, effective delivery when used correctly. Proper site selection and rotation are fundamental to successful long-term treatment. This guide provides evidence-based advice on injection sites, technique, and managing common reactions in line with UK clinical guidance.

Where to Inject Mounjaro: Approved Injection Sites

Mounjaro (tirzepatide) is a once-weekly subcutaneous injection licensed in the UK for the treatment of type 2 diabetes mellitus and, more recently, for weight management in adults with obesity or overweight with weight-related comorbidities. Understanding the correct injection sites is essential for ensuring optimal drug absorption, minimising discomfort, and reducing the risk of injection site complications.

The three approved injection sites for Mounjaro are:

• Abdomen (stomach area) – the preferred site for many patients, avoiding a 5 cm radius around the navel

• Thigh (front or outer area) – the upper, outer portion of the thigh provides good subcutaneous tissue

• Upper arm (back of the arm) – the fatty tissue at the back of the upper arm, though this site typically requires assistance from another person for safe administration

These sites have been selected because they contain adequate subcutaneous fat tissue, which allows for consistent absorption of tirzepatide. The medication must be injected into the subcutaneous (fatty) layer—not into muscle (intramuscular) or into the skin (intradermal)—to ensure it works as intended. Intramuscular injection is not recommended.

It is important to avoid injecting into areas that are sore, bruised, scarred or hard. Patients should also avoid injecting into areas with lumps, nodules, or lipohypertrophy (thickened fatty tissue), as these can impair drug absorption. If you have a skin condition such as eczema or psoriasis affecting potential injection sites, consult your healthcare professional for advice. Always inspect the injection site before administering Mounjaro and choose a healthy area of skin with sufficient subcutaneous tissue.

How to Choose the Best Injection Site for Mounjaro

Selecting the most appropriate injection site for each dose of Mounjaro involves considering several practical and clinical factors. When used correctly, all three approved sites—abdomen, thigh, and upper arm—can provide effective delivery of the medication, with no clinically meaningful differences in absorption reported between sites.

The abdomen is often the easiest site for self-injection, as it is readily accessible and typically has ample subcutaneous fat. Most patients find it comfortable and straightforward to inject into the stomach area. However, it is essential to avoid the area within 5 cm of the navel, as recommended in the Patient Information Leaflet.

The thigh is another excellent option, particularly for patients who prefer not to inject into the abdomen or who have limited abdominal subcutaneous tissue. The front or outer portion of the thigh should be used, avoiding the inner thigh where there is less fat and more muscle. This site is also convenient for self-administration and allows for easy visualisation during injection.

The upper arm may be more challenging for self-injection, as reaching the back of the arm can be difficult without assistance. This site is generally not recommended for self-administration and is best suited for patients who have a carer, family member or healthcare professional who can help administer the injection. It is important to use the fatty tissue at the back of the upper arm, not the shoulder or the area close to the elbow.

Patients should also consider personal comfort, ease of access, and any existing skin conditions when choosing an injection site. Those with a higher body mass index (BMI) may have more subcutaneous tissue available across all sites, while leaner individuals may find the abdomen or thigh more suitable. Rotating sites regularly is essential to prevent tissue damage and maintain consistent drug absorption.

Rotating Injection Sites: Why It Matters

Rotating injection sites is a critical practice for anyone using Mounjaro or other subcutaneous medications on a long-term basis. Repeatedly injecting into the same area can lead to a range of complications that may compromise both the effectiveness of the medication and the health of the skin and underlying tissue.

One of the most common issues associated with poor site rotation is lipohypertrophy—a localised thickening or lumping of fatty tissue caused by repeated trauma to the same injection site. Lipohypertrophy not only causes cosmetic concerns but can also impair drug absorption. Studies with insulin have shown that injecting into areas of lipohypertrophy can lead to variable absorption and unpredictable effects. While specific data for tirzepatide is limited, similar principles of good injection technique apply.

In addition to lipohypertrophy, repeated injections in the same site can cause bruising, tenderness, scarring, and localised inflammation. These changes can make future injections more painful and may increase the risk of injection site reactions such as erythema (redness), swelling, or itching.

Best practices for site rotation include:

• Using a different injection site each week (e.g., alternating between abdomen, thigh, and upper arm)

• Within each site, moving the injection point by at least 2–3 cm from the previous injection

• Keeping a simple log or mental note of where the last injection was given

• Inspecting all potential sites regularly for signs of tissue damage or skin changes

Patients should be reassured that Mounjaro can be injected into any of the three approved sites without affecting efficacy, provided the sites are rotated appropriately. Healthcare professionals should provide clear, practical guidance on site rotation during initiation of therapy and at follow-up appointments.

Step-by-Step Guide to Injecting Mounjaro Safely

Administering Mounjaro correctly is essential for ensuring patient safety, maximising therapeutic benefit, and minimising the risk of complications. The following step-by-step guide is based on the manufacturer's instructions for the single-dose pre-filled pen.

Before injection:

• Check the medication – Remove the Mounjaro pen from the refrigerator and allow it to reach room temperature (approximately 30 minutes). Do not use the pen if it has been frozen or exposed to excessive heat.

• Inspect the pen – Check the expiry date and ensure the solution is clear and colourless. Do not use if the liquid appears cloudy, discoloured, or contains particles.

• Wash your hands thoroughly with soap and water.

• Choose and prepare the injection site – Select one of the three approved sites (abdomen, thigh, or upper arm) and clean the area with an alcohol wipe. Allow the skin to dry completely before injecting.

During injection:

• Remove the base cap from the Mounjaro pen.

• Place the clear base flat against your skin at the chosen injection site.

• Unlock the pen by turning the lock ring.

• Press and hold the injection button firmly.

• Listen for the first click, then continue to hold until you hear a second click.

• Keep holding the button for 10 seconds after the second click to ensure the full dose is delivered.

• Remove the pen from your skin after the 10 seconds.

After injection:

• Dispose of the used pen safely in a sharps container. You can obtain a sharps bin from your GP surgery or pharmacy, and they can advise on local arrangements for returning filled containers.

• Monitor the injection site for any immediate reactions such as redness, swelling, or discomfort.

• Record the injection site and date to assist with site rotation.

Always read the Patient Information Leaflet and Instructions for Use that come with your medication for the most up-to-date guidance.

Contact your GP, diabetes specialist nurse or NHS 111 if you experience persistent pain, significant swelling, signs of infection (warmth, pus, fever), or difficulty injecting. For severe allergic reactions such as widespread rash, difficulty breathing, or swelling of the face or throat, call 999 or go to A&E immediately.

Common Injection Site Reactions and How to Manage Them

Injection site reactions are among the commonly reported adverse effects associated with Mounjaro. According to the Summary of Product Characteristics, injection site reactions are classified as 'common' (may affect up to 1 in 10 people). Understanding how to recognise and manage these reactions is important for patient safety and adherence to treatment.

Common injection site reactions include:

• Erythema (redness) – usually appears within minutes to hours of injection and typically resolves within 24–48 hours

• Swelling or induration (hardness) – may persist for several days but should gradually improve

• Itching or mild discomfort – often transient and manageable with simple measures

• Bruising – more common in patients taking anticoagulants or antiplatelet agents, or those with fragile skin

Management strategies for mild injection site reactions include:

• Applying a cold compress (not ice directly on skin) to reduce swelling and discomfort

• Avoiding rubbing or scratching the injection site

• Using a different injection site for the next dose

• Ensuring proper injection technique, including allowing the skin to dry after cleaning

Patients should be advised to contact their GP or healthcare provider if they experience:

• Severe or worsening pain at the injection site

• Signs of infection such as increasing redness, warmth, pus, or fever

• Persistent swelling or lumps that do not resolve within a week

• Allergic reactions such as widespread rash, difficulty breathing, or swelling of the face or throat (call 999 or go to A&E immediately)

There is no established link between injection site reactions and reduced efficacy of Mounjaro, but persistent reactions may indicate poor injection technique or the need for site rotation. Healthcare professionals should review injection technique with patients experiencing recurrent site reactions and consider referral to a diabetes specialist nurse for additional support and education.

Patients are encouraged to report any suspected side effects to the MHRA Yellow Card Scheme at yellowcard.mhra.gov.uk or search for 'MHRA Yellow Card' in the Google Play or Apple App Store.

Frequently Asked Questions