Tirzepatide is a dual glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptor agonist used for type 2 diabetes and weight management in the UK. The medication should appear clear and colourless to slightly yellow when properly stored. If your tirzepatide appears red or pink, this indicates the product may be compromised and should not be used. Understanding normal appearance, potential causes of discolouration, and proper storage is essential for safe medication use. This article explains why tirzepatide might turn red and what action to take.
Quick Answer: Red or pink discolouration in tirzepatide indicates the medication has been compromised and should never be used.
Tirzepatide is a 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 (as Mounjaro) and for weight management (as Zepbound) in adults with obesity or overweight with at least one weight-related comorbidity. The medication is supplied as a sterile, preservative-free solution in single-dose pre-filled pens for subcutaneous injection.
According to the Medicines and Healthcare products Regulatory Agency (MHRA) approved Summary of Product Characteristics (SmPC), tirzepatide solution should appear clear and colourless to slightly yellow. This is the expected appearance for a properly stored, unexpired product. The solution should be free from visible particles, cloudiness, or any unusual discolouration. Before each injection, patients should inspect the medication visually through the pen's inspection window.
Any deviation from this normal appearance—including the presence of particles, cloudiness, or unexpected colour changes—may indicate that the medication has been compromised. The MHRA and manufacturers emphasise the importance of visual inspection as a critical safety step before administration. If the solution appears abnormal in any way, it should not be used, and patients should contact their GP, pharmacist or diabetes/weight management team for guidance.
It is worth noting that slight variations in colour intensity (from completely colourless to a faint yellow tinge) can occur between batches and are considered acceptable. However, any pronounced colour change, particularly to red, pink, brown, or any other unexpected hue, falls outside the normal specification and requires immediate attention. Always check the expiry date and do not use pens with damaged packaging.
A red or pink discolouration in tirzepatide is not a normal characteristic of the medication and suggests that the product may have been compromised. While there is no officially documented specific mechanism for red discolouration in tirzepatide, several general factors can potentially cause such changes in biological medications.
Potential general causes of discolouration in biological medicines include:
Temperature excursions: Exposure to temperatures outside the recommended storage range (particularly heat) can cause protein degradation and chemical changes that may alter the solution's appearance
Contamination: Though rare in unopened sterile products, introduction of foreign substances or particulate matter could potentially cause colour changes
Chemical degradation: Oxidation or other chemical reactions affecting the peptide structure may result in discolouration
Manufacturing defects: Though rare, quality control issues during production could theoretically result in off-specification products
Interaction with packaging materials: In exceptional circumstances, degradation of pen components or seals might introduce coloured substances into the solution
It is important to note that biological medications like tirzepatide are particularly sensitive to environmental conditions. The peptide structure can be altered by factors such as light exposure, temperature fluctuations, physical agitation, or prolonged storage beyond expiry dates.
Patients who observe red or any other unusual discolouration should not use the medication. The altered appearance indicates that the product's integrity cannot be guaranteed, and administration could pose safety risks or result in reduced therapeutic efficacy. Note the batch/lot number of the affected pen and contact your pharmacist or prescriber for advice.
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Start HereDiscoloured tirzepatide should never be used. This is a fundamental safety principle that applies to all injectable biological medications and is explicitly stated in the product's SmPC. When a medication's appearance deviates from its specified characteristics, it indicates that the product may have undergone physical, chemical, or biological changes that could compromise both safety and efficacy.
The primary concerns with using discoloured tirzepatide include:
Loss of therapeutic effect: Degradation of the active peptide may render the medication ineffective, leading to inadequate glycaemic control or failure to achieve intended weight management outcomes
Potential toxicity: Degradation products or contaminants responsible for the colour change may pose direct health risks
Immunogenicity: Altered protein structures can potentially trigger unwanted immune responses
Infection risk: If discolouration results from contamination, injection could introduce harmful substances into subcutaneous tissue
If you discover discoloured tirzepatide, you should:
If you have inadvertently used discoloured tirzepatide and experience symptoms of a severe allergic reaction (such as difficulty breathing, swelling of face/throat, or severe rash), call 999 or go to A&E immediately. For less severe concerns after using discoloured medication, contact your GP or NHS 111 for advice.
Your healthcare team can provide guidance on managing your diabetes or weight management regimen whilst awaiting replacement medication, including advice on missed doses.
Proper storage of tirzepatide is essential to maintain its stability, efficacy, and safety throughout its shelf life. As a biological medication containing a sensitive peptide structure, tirzepatide requires specific storage conditions to prevent degradation.
Storage requirements for tirzepatide pens according to the SmPC:
Store in a refrigerator at 2°C to 8°C
Keep in the original carton to protect from light
Do not freeze; if accidentally frozen, the medication must be discarded
Do not shake
Keep away from the freezer compartment
Important: Tirzepatide pens are for single use only. Each pen is designed to deliver a single dose and must be disposed of after one injection, even if medication appears to remain in the pen.
Temporary storage outside the refrigerator:
If needed, unopened tirzepatide pens may be stored at temperatures up to 30°C for up to 21 days before use. After this period, the pen must be used or discarded. This allowance applies only to unopened pens, not to pens after injection.
Additional storage precautions:
Never store tirzepatide in direct sunlight or near heat sources (radiators, windowsills, car dashboards)
Avoid storing in bathrooms where temperature and humidity fluctuate
Keep out of reach of children
When travelling, use an insulated cooling bag if refrigeration is unavailable, ensuring the medication does not freeze
Before injection, allow the pen to reach room temperature (approximately 30 minutes out of the refrigerator) to improve comfort and reduce injection site reactions. Always inspect the solution visually before use—if it appears red, cloudy, discoloured, or contains particles, do not use it.
If you have concerns about whether your tirzepatide has been stored correctly, or if you are unsure about its appearance, contact your pharmacist, GP or diabetes/weight management team before administration. Proper storage practices significantly reduce the risk of medication degradation and ensure optimal therapeutic outcomes.
Tirzepatide should appear clear and colourless to slightly yellow. Any red, pink, brown, or other unexpected discolouration indicates the medication may be compromised and should not be used.
No, you should never use discoloured tirzepatide. Red discolouration suggests degradation or contamination, which may compromise safety and efficacy. Contact your pharmacist or GP immediately for a replacement.
Store tirzepatide in a refrigerator at 2–8°C in its original carton to protect from light. Never freeze or shake the pen. Unopened pens may be kept at up to 30°C for up to 21 days if needed.
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DisclaimerThis content is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional with any medical questions or concerns. Use of the information is at your own risk, and we are not responsible for any consequences resulting from its use.
