Mounjaro (tirzepatide) is a once-weekly injectable medication for type 2 diabetes, supplied as a pre-filled, single-use pen. Understanding how to open Mounjaro correctly is essential for safe, effective administration. The pen features a simple design: removing the clear base cap unlocks the device, making it ready for immediate subcutaneous injection. No separate needle attachment is required, and the needle remains safely concealed throughout. This guide provides step-by-step instructions on opening your Mounjaro pen, preparing for injection, troubleshooting common issues, and ensuring proper storage and disposal in line with UK clinical guidance.

What Is Mounjaro and How Is It Supplied?

Mounjaro (tirzepatide) is a once-weekly injectable medication licensed in the UK for the treatment of type 2 diabetes mellitus in adults. It belongs to a class of medicines known as dual glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptor agonists. By activating both GIP and GLP-1 receptors, Mounjaro enhances insulin secretion when blood glucose levels are elevated, suppresses glucagon release, slows gastric emptying, and reduces appetite—collectively improving glycaemic control and potentially supporting weight loss as part of diabetes management.

Mounjaro is supplied as a pre-filled, single-use pen injector designed for subcutaneous (under the skin) administration only. Each pen contains a fixed dose of tirzepatide solution and is available in several strengths: 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, and 15 mg per 0.5 mL. The pen features an automatic injection mechanism that does not require manual needle attachment or dose dialling by the patient.

The pen arrives ready to use, with the needle concealed inside a protective cap. There is no need to attach a separate needle, as is required with some other injectable diabetes medications. Each pen is intended for a single injection only and must be disposed of safely after use, even if some solution remains. Patients should always check the pen's label to confirm the correct dose has been dispensed by their pharmacy, and inspect the solution through the viewing window to ensure it is clear and colourless before administration.

Importantly, Mounjaro pens are for personal use only and should never be shared with others, even if the needle is changed, due to the risk of cross-infection.

Step-by-Step Guide to Opening Your Mounjaro Pen

Opening your Mounjaro pen correctly is essential to ensure safe and effective administration. The process is straightforward and involves removing protective components in the correct sequence.

Step 1: Remove the pen from the refrigerator Take the pen out of refrigerated storage and allow it to reach room temperature naturally for approximately 30 minutes before use. Do not attempt to warm the pen artificially using a microwave, hot water, or direct sunlight, as this may damage the medication.

Step 2: Wash your hands thoroughly Clean your hands with soap and water to reduce the risk of infection at the injection site.

Step 3: Inspect the pen Check the label to confirm you have the correct dose. Look through the viewing window to ensure the solution is clear and colourless. Do not use the pen if the liquid appears cloudy, discoloured, or contains particles, or if the pen appears damaged.

Step 4: Remove the base cap Hold the pen firmly and pull off the clear base cap straight away from the pen body. Do not twist the cap, as this is unnecessary and may cause confusion. Set the base cap aside; you will not replace it.

Step 5: The pen is now ready Once the base cap is removed, the pen is unlocked and ready for immediate injection. Do not delay using the pen once the cap is removed. The needle remains safely concealed inside the pen until you press it against your skin. Do not remove or attempt to access the needle manually, and avoid touching the needle guard—the pen's design ensures the needle only extends during injection and retracts automatically afterwards for safety.

If you have dexterity or vision issues, consider asking your diabetes nurse or pharmacist for additional training on using the Mounjaro pen.

Preparing Mounjaro for Injection

After successfully opening your Mounjaro pen, proper preparation ensures a safe and comfortable injection experience.

Selecting an injection site Mounjaro should be injected subcutaneously into areas with adequate fatty tissue. The recommended sites are:

• Abdomen (at least 5 cm away from the navel)

• Thigh (front or outer area)

• Upper arm (back or outer area—should be administered by another person)

Rotate injection sites with each weekly dose to minimise the risk of lipodystrophy (changes in fatty tissue) and injection site reactions. Avoid injecting into areas that are tender, bruised, red, hard, or scarred.

Cleaning the injection site Wipe the chosen area with an alcohol swab and allow the skin to dry completely before proceeding. Injecting into damp skin may cause stinging.

Positioning the pen Hold the pen with the clear base pointing downward toward your skin. Place the base flat and firmly against your skin at a 90-degree angle. Do not hold the pen at an angle, as this may result in incomplete injection.

Administering the injection Press the pen firmly against your skin until you hear the first click, which indicates the injection has started. Continue holding the pen in place until you hear a second click (usually after about 5–10 seconds), which signals the injection is complete. You may see a grey plunger moving in the viewing window during injection.

After injection Lift the pen straight away from your skin. The needle will retract automatically back into the pen. A small amount of blood or clear fluid at the injection site is normal—apply gentle pressure with a clean tissue or cotton wool if needed, but do not rub the area.

Common Issues When Opening Mounjaro and Solutions

While the Mounjaro pen is designed for simplicity, patients occasionally encounter difficulties. Understanding common issues and their solutions can prevent anxiety and ensure successful administration.

Issue 1: Difficulty removing the base cap Some patients find the base cap tight or difficult to remove. Solution: Grip the pen body firmly with one hand and pull the base cap straight off with steady, even pressure—avoid twisting. If you have limited hand strength or dexterity, ask a family member or carer to assist, or consult your practice nurse for a demonstration.

Issue 2: Pen feels cold or uncomfortable Injecting cold medication can cause discomfort. Solution: Always allow the pen to reach room temperature (approximately 30 minutes) before use. Never use external heat sources. If you forget to remove the pen from the refrigerator in advance, wait the full 30 minutes rather than rushing.

Issue 3: Unsure if the injection was completed Patients sometimes worry they did not hold the pen long enough. Solution: Always wait for the second click and observe the grey plunger reaching the end of the viewing window. If you are uncertain whether the full dose was delivered, do not inject again. Contact your GP or diabetes specialist nurse for advice—administering a double dose could increase the risk of adverse effects such as nausea or, particularly if you also take insulin or sulfonylureas, hypoglycaemia (low blood sugar).

Issue 4: Pen appears damaged or solution looks abnormal Occasionally, pens may be dropped or the solution may appear cloudy. Solution: Do not use a damaged pen or one with abnormal-looking solution. Return it to your pharmacy for replacement and report the issue. Suspected device defects should be reported to the MHRA Yellow Card scheme and the manufacturer.

Issue 5: Needle anxiety or injection site reactions Some patients experience anxiety about self-injection or develop mild redness at injection sites. Solution: The Mounjaro pen conceals the needle throughout, which many patients find reassuring. For persistent anxiety, speak with your diabetes nurse about injection technique training or psychological support. Mild injection site reactions (redness, itching) usually resolve within a few days—rotate sites and apply a cool compress if needed. Contact your GP if reactions are severe or persistent.

Important safety note: If you experience severe, persistent abdominal pain (with or without vomiting), stop taking Mounjaro and seek urgent medical advice as this could indicate pancreatitis. Also seek medical advice for symptoms of gallstones or severe dehydration.

Safe Storage and Disposal After Opening

Proper storage before use and safe disposal after injection are essential components of responsible medication management.

Storage before opening Unused Mounjaro pens must be stored in a refrigerator at 2°C to 8°C. Keep the pen in its original carton to protect it from light. Do not freeze Mounjaro—if a pen has been frozen, it must be discarded. If refrigeration is temporarily unavailable (e.g., during travel), Mounjaro may be stored at room temperature (not exceeding 30°C) for up to 21 days. After this period, the pen must be discarded even if unused. Always check the expiry date printed on the pen and carton—do not use Mounjaro beyond this date.

After removing the base cap Once the base cap is removed, the pen should be used immediately. Do not replace the base cap, as this may damage the needle mechanism inside. If you remove the cap but cannot complete the injection immediately, the pen should be discarded—it is not designed to be stored after the cap has been removed.

Safe disposal After injection, the used pen must be disposed of safely in a sharps container. These puncture-resistant containers are available from your GP surgery, pharmacy, or local council, though availability and costs may vary depending on your location. Never throw used pens in household rubbish or recycling bins, as this poses a needlestick injury risk to waste handlers. Do not attempt to remove or recap the needle. When your sharps container is three-quarters full, seal it and return it according to local guidelines, which your healthcare provider or local council can explain.

Patient safety advice Keep all Mounjaro pens out of sight and reach of children. If accidental injection occurs, contact NHS 111 for urgent clinical advice; call 999 only if severe symptoms develop (such as collapse or severe breathing difficulty). If you miss a dose and it has been fewer than four days since the missed dose was due, inject as soon as possible; if more than four days have passed, skip the missed dose and resume your regular schedule. Alternatively, you can change your weekly dosing day provided there are at least 3 days (72 hours) between doses. Contact your diabetes team if you have questions about missed doses or experience persistent adverse effects.

Report suspected side effects to the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk.

Frequently Asked Questions