Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist licensed in the UK for type 2 diabetes mellitus, administered via once-weekly subcutaneous injection. Many patients wonder whether Mounjaro can be injected in the arm, particularly if they wish to rotate injection sites or find other areas less accessible. The upper arm is indeed an approved injection site alongside the abdomen and thigh, offering flexibility in treatment administration. However, arm injections typically require assistance from another person or healthcare professional due to the difficulty in reaching the correct area safely. Understanding proper injection technique, site rotation, and potential local reactions is essential for safe and effective use of this medication.

Can Mounjaro Be Injected in the Arm?

Yes, Mounjaro (tirzepatide) can be injected into the upper arm, making it one of three approved injection sites for this medication. Tirzepatide is a dual glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptor agonist licensed in the UK for the treatment of type 2 diabetes mellitus. Tirzepatide is also available under the brand name Zepbound for weight management in adults with obesity or overweight with weight-related comorbidities.

The upper arm is a convenient and effective site for subcutaneous administration, particularly for patients who prefer variety in their injection routine or find other sites less accessible. The medication is designed for once-weekly subcutaneous injection, and the flexibility of injection sites—including the arm—helps patients maintain adherence to their treatment regimen whilst minimising localised skin reactions.

It is important to note that arm injections typically require assistance from another person or a healthcare professional, as reaching the correct area of the upper arm can be challenging when self-administering. Patients should receive appropriate training from their GP, practice nurse, or diabetes specialist nurse before attempting injections in the arm, particularly if this is their first time using this site. The MHRA-approved prescribing information confirms that the abdomen, thigh, and upper arm are all suitable injection sites, and you should follow the specific guidance in the Patient Information Leaflet for your medication.

Approved Injection Sites for Mounjaro

Mounjaro is licensed for subcutaneous injection in three specific anatomical areas: the abdomen, the thigh, and the upper arm. Each site has been evaluated to ensure the medication can be administered safely and effectively.

The abdomen offers a large surface area with adequate subcutaneous fat and is easily accessible for self-injection. Patients should inject into the abdominal area at least 5 centimetres away from the navel (belly button) and avoid areas with scars, bruises, or skin abnormalities.

The thigh provides another accessible option for self-administration. This site is particularly useful for patients who find abdominal injections uncomfortable or who have limited abdominal subcutaneous tissue.

The upper arm is the third approved site. As mentioned, this site usually requires assistance from another person due to the difficulty in reaching and stabilising the area during injection.

Patients can choose their injection site based on personal preference, comfort, and practical considerations. The prescribing information emphasises that patients should rotate injection sites weekly to reduce the risk of local skin reactions. Always follow the specific instructions in your Patient Information Leaflet regarding site selection and rotation.

How to Inject Mounjaro in Your Upper Arm Safely

Administering Mounjaro into the upper arm requires careful technique and, in most cases, the assistance of a trained caregiver or healthcare professional. Proper injection technique is essential to ensure the medication is delivered correctly.

Step-by-step guidance for upper arm injection:

• Identify the correct site: Locate the upper arm where there is adequate subcutaneous fat. If the tissue feels too thin or muscular, consider using an alternative site.

• Prepare the injection: Remove the Mounjaro pen from the refrigerator and allow it to reach room temperature as directed in the Patient Information Leaflet, which can reduce injection discomfort. Check the medication is clear and colourless; do not use if it appears cloudy or discoloured.

• Clean the site: Use an alcohol wipe to cleanse the injection area and allow it to dry completely. This reduces the risk of infection.

• Administer the injection: The Mounjaro pen should be placed flat against the skin at a 90-degree angle. Follow the specific instructions for your pen, including unlocking the device, pressing the injection button, and holding until the indicator stops moving or you hear the second click (usually up to 10 seconds) to ensure complete dose delivery.

• Dispose safely: After use, dispose of the entire pen in a UK-approved sharps bin. These can be obtained from your GP surgery, pharmacy or local council. Never dispose of used pens in household waste.

Patients should never inject into areas with active skin conditions, such as eczema, psoriasis, or infection. If you experience persistent pain, bleeding, or signs of infection following an injection, contact your GP or diabetes care team promptly.

Rotating Injection Sites: Why It Matters

Regular rotation of injection sites is a critical aspect of safe and effective Mounjaro therapy. Rotating the site with each weekly dose helps minimise local skin reactions and ensures consistent absorption of the medication.

Repeated injections into the same area can potentially lead to changes in the subcutaneous tissue. These changes not only affect cosmetic appearance but can also affect medication absorption, potentially reducing therapeutic efficacy.

Best practices for site rotation include:

• Use a different injection site each week, cycling through the abdomen, thigh, and upper arm systematically.

• Within each anatomical area, vary the precise injection point. For example, if injecting into the abdomen one week, use the right side; the following week, use the left side.

• Keep a simple injection diary or use a smartphone app to track which sites have been used and when. Many patients find it helpful to follow a consistent pattern (e.g., abdomen week 1, right thigh week 2, left thigh week 3, upper arm week 4).

• Inspect injection sites regularly for signs of skin changes, bruising, redness, or tenderness. If abnormalities develop, avoid that area until it has fully healed.

Your diabetes specialist nurse can provide personalised advice and demonstrate proper rotation strategies during routine appointments. Following good injection technique and site rotation practices helps ensure you receive the full benefit from your medication.

Common Side Effects at the Injection Site

Local injection site reactions are generally mild and transient with Mounjaro, though patients should be aware of what to expect and when to seek medical advice. In clinical trials, injection site reactions occurred in a small percentage of participants and were typically self-limiting.

Common injection site reactions include:

• Mild pain or discomfort: A brief stinging or burning sensation during or immediately after injection is normal and usually resolves within minutes. Allowing the medication to reach room temperature before injection can minimise discomfort.

• Redness (erythema): Slight redness at the injection site, typically less than 2–3 centimetres in diameter, may appear and usually fades within a few hours to a day.

• Bruising: Small bruises can occur if a capillary is inadvertently punctured during injection. This is more common in patients taking anticoagulant or antiplatelet medications. Applying gentle pressure (without rubbing) immediately after injection can help minimise bruising.

• Itching or mild swelling: Localised itching or a small raised area at the injection site may develop but typically resolves without intervention. If itching is severe or accompanied by a spreading rash, this may indicate a hypersensitivity reaction requiring medical assessment.

When to contact your healthcare professional:

• Persistent pain, significant swelling, or warmth at the injection site lasting more than 48 hours

• Signs of infection, including increasing redness, pus, or fever

• Development of hard lumps or significant changes in skin texture

• Severe allergic reactions, such as widespread rash, difficulty breathing, or facial swelling (seek emergency care immediately)

Serious injection site reactions are rare with Mounjaro. However, patients should report any concerning symptoms to their GP or diabetes care team. You can report suspected side effects via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk or through the Yellow Card app. Most local reactions can be managed conservatively with site rotation, proper injection technique, and basic wound care.

Frequently Asked Questions