Mounjaro (tirzepatide) is a once-weekly injectable medication licensed in the UK for type 2 diabetes mellitus and weight management in adults with obesity or overweight with weight-related comorbidities. Understanding the shelf life of Mounjaro is crucial for ensuring your medication remains safe and effective. Unopened pens remain stable until the manufacturer's expiry date when stored correctly, whilst opened pens are single-use devices that must be discarded immediately after administration. Proper storage—either refrigerated between 2°C and 8°C or at room temperature (≤30°C) for up to 21 days—maintains the medication's potency and therapeutic efficacy.

What Is the Shelf Life of Mounjaro?

Mounjaro (tirzepatide) is a once-weekly injectable medication licensed in the UK for the treatment of type 2 diabetes mellitus. It is also licensed for weight management in adults with obesity or overweight with weight-related comorbidities, subject to specific NHS criteria. Understanding the shelf life of Mounjaro is essential for ensuring the medication remains safe and effective.

Unopened Mounjaro pens have a shelf life that extends until the expiry date printed on the carton and pen label by the manufacturer. This date is determined through stability testing conducted by Eli Lilly and Company, ensuring the medication maintains its potency and safety when stored under recommended conditions. Always check the specific expiry date on your individual pens.

Important: Mounjaro pens are single-use devices. Each pen delivers one dose only and must be discarded immediately after use in a proper sharps container. There is no storage period after the pen has been used.

If an unopened pen is removed from the refrigerator, it can be stored at room temperature (not exceeding 30°C) for up to 21 days before use. If you choose to store an unopened pen at room temperature, it's advisable to note the date you removed it from the refrigerator to ensure you use it within this 21-day window.

Using expired medication may result in reduced efficacy, as the active ingredient tirzepatide may degrade over time, potentially leading to inadequate glycaemic control or insufficient weight management. Always consult your healthcare provider or pharmacist if you have concerns about the shelf life of your Mounjaro prescription.

How to Store Mounjaro Correctly

Proper storage of Mounjaro is vital to maintain the medication's stability, efficacy, and safety. Tirzepatide is a glucagon-like peptide-1 (GLP-1) receptor agonist and glucose-dependent insulinotropic polypeptide (GIP) receptor agonist, which means it is a biological peptide that can be sensitive to environmental conditions such as temperature and light.

Unopened Mounjaro pens should be stored in a refrigerator at temperatures between 2°C and 8°C. The pens should be kept in their original carton to protect them from light exposure, which can degrade the active ingredient. Never store Mounjaro in the freezer, and if a pen has been accidentally frozen, it must be discarded and not used, even if it has thawed.

Alternatively, unopened pens may be kept at room temperature (not exceeding 30°C) for up to 21 days before use. Many patients find room temperature injections more comfortable. If you choose this option, record the date you removed the pen from the refrigerator to track the 21-day limit.

Remember that Mounjaro pens are single-use devices. After administering your dose, the pen should be immediately disposed of in a proper sharps container. You cannot store a pen after it has been used.

Additional storage guidance includes keeping Mounjaro away from direct heat sources such as radiators, windowsills with direct sunlight, or hot vehicles. The pen should always be stored with the cap on to protect it from light and contamination. Keep all medications out of the sight and reach of children. If you are travelling, consider using an insulated medication travel case with cooling elements to maintain appropriate temperatures, particularly during warm weather. Always transport your Mounjaro in hand luggage when flying, as cargo holds can experience freezing temperatures.

Ask your healthcare provider or pharmacist about obtaining a sharps bin for safe disposal of used pens.

Does Mounjaro Need to Be Refrigerated?

The refrigeration requirements for Mounjaro depend on your storage preferences and personal circumstances. Understanding these requirements helps ensure optimal medication efficacy whilst providing flexibility for daily life.

Unopened Mounjaro pens must be refrigerated at temperatures between 2°C and 8°C until you are ready to use them, unless you choose the room temperature storage option. Refrigeration is essential to maintain the stability of tirzepatide, the active pharmaceutical ingredient. Refrigeration slows the degradation process that naturally occurs with peptide-based medications, ensuring the drug maintains its full potency until the expiry date. When you collect your prescription from the pharmacy, it should be transported home promptly and placed in the refrigerator. If you anticipate a delay, ask your pharmacist for a cool bag or insulated packaging.

Alternatively, unopened pens can be stored at room temperature (not exceeding 30°C) for up to 21 days before use. This flexibility is particularly helpful for patients who travel frequently or have limited refrigerator space. If you choose this option, it's important to keep track of when you removed the pen from the refrigerator to ensure you use it within the 21-day period.

Important: Mounjaro pens are single-use devices. After administering your dose, the pen must be discarded immediately in a proper sharps container. There is no storage period after the pen has been used.

Many patients find that injecting Mounjaro at room temperature is more comfortable than using cold medication directly from the refrigerator. If you store your pen in the refrigerator, you may wish to remove it before injection to allow it to warm naturally to room temperature. Never attempt to warm the pen artificially using hot water, microwaves, or other heat sources, as this can damage the medication. Always ensure the pen is stored safely with the cap on and away from direct light and heat sources.

What Happens If Mounjaro Expires or Is Stored Incorrectly?

Using expired or improperly stored Mounjaro can compromise treatment outcomes and potentially pose safety concerns. Understanding the risks helps patients make informed decisions and maintain medication efficacy.

Expired Mounjaro should never be used, even if it appears normal. After the expiry date, the chemical stability of tirzepatide cannot be guaranteed. The medication may have degraded, resulting in reduced potency and diminished therapeutic effect. For patients with type 2 diabetes, this could mean inadequate blood glucose control, increasing the risk of hyperglycaemia and associated complications. For those using Mounjaro for weight management, reduced efficacy may result in suboptimal weight loss outcomes.

Incorrect storage conditions can similarly compromise the medication. If Mounjaro has been frozen, exposed to temperatures above 30°C, or left in direct sunlight, the molecular structure of tirzepatide may be altered. Frozen medication must always be discarded, even after thawing. Unopened pens kept at room temperature (≤30°C) for more than 21 days should not be used. If you suspect your Mounjaro has been exposed to inappropriate temperatures (for example, left in a hot car or outside the refrigerator for an extended period), contact your pharmacist for advice before using it.

Disposal of expired or compromised Mounjaro should follow proper pharmaceutical waste guidelines. Used pens should be placed in a designated sharps container. When your sharps container is nearly full, follow local NHS guidelines for disposal—this may involve returning it to your GP surgery, local pharmacy, or council collection service. Never dispose of Mounjaro pens in household waste or down drains, as this can harm the environment and pose a risk to others.

If you have used expired medication inadvertently, monitor your blood glucose levels closely (if diabetic) and contact your GP or diabetes specialist nurse for guidance. You may require additional monitoring or an earlier review to ensure your condition remains well controlled.

If you experience any side effects from Mounjaro, report them via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk.

Checking Your Mounjaro Pen Before Use

Performing a visual inspection of your Mounjaro pen before each injection is an essential safety step that helps identify potential problems with the medication. This simple check takes only moments but can prevent administration of compromised medication.

Visual inspection procedure: Before each injection, remove the Mounjaro pen from storage and examine it carefully. Look through the viewing window on the pen to inspect the solution. Mounjaro should be clear and colourless to slightly yellow. The solution should be free from visible particles, cloudiness, or discolouration. If you notice any particles floating in the liquid, cloudiness, or a change in colour, do not use the pen. Similarly, check that the liquid is present in the cartridge and that the pen does not appear damaged or cracked.

Check the expiry date printed on the pen label before every use. Verify that the medication has not passed its expiry date. If you've been storing an unopened pen at room temperature, ensure you are within the 21-day window since removing it from the refrigerator.

Remember that Mounjaro pens are single-use devices with a hidden, non-detachable needle. You do not need to attach or inspect a separate needle before use.

Additional safety checks include ensuring the pen cap is intact and that the pen has been stored correctly. If the pen has been dropped or appears damaged in any way, do not use it. If you have any concerns about the appearance of your Mounjaro pen, the integrity of the medication, or whether it has been stored correctly, do not use it. Contact your pharmacist or healthcare provider for advice. They can assess whether you need a replacement prescription.

Never share your Mounjaro pen with another person, even if the needle has been changed, as this carries a risk of infection transmission. After use, immediately dispose of the pen in a proper sharps container.

Your diabetes specialist nurse or practice nurse can provide additional guidance on proper pen inspection and injection technique if needed.

Frequently Asked Questions