Getting started with weight loss injections can feel daunting, especially when your Mounjaro pen doesn't seem to cooperate. Whether you're experiencing a jammed pen, dosing difficulties, or storage concerns, understanding how to troubleshoot common issues ensures you continue your weight loss journey safely and effectively. As a GPhC-registered online pharmacy, Happy Pharmacy provides the support and guidance you need to use your Mounjaro injection pen with confidence.
Understanding Your Mounjaro Pen: The Basics
Mounjaro (tirzepatide) represents a significant breakthrough in weight loss treatment, with clinical trials demonstrating average weight loss of 15-20% of body weight over 72 weeks. The medication comes in a pre-filled, single-dose pen designed for subcutaneous injection, making weekly treatment convenient for patients across the UK. However, like any medical device, the injection pen occasionally encounters operational issues that can disrupt your treatment schedule.
The pen's design incorporates several safety features to protect users, but these same mechanisms can sometimes cause confusion when things don't work as expected. Understanding the pen's components and common failure points helps you identify problems quickly and maintain your treatment consistency.
Most Common Mounjaro Pen Problems and Solutions
The Pen Won't Inject or Feels Jammed
One of the most frequently reported issues involves the pen feeling stuck or refusing to deliver the dose. This typically occurs when the injection button won't depress fully, or you feel unusual resistance during injection.
Primary causes include:
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The pen hasn't been properly prepared before injection. Each Mounjaro pen requires specific preparation steps, including removing the base cap and attaching a new needle before each use. If you attempt to inject without completing these steps, the pen's safety mechanisms prevent activation.
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The medication is too cold. Injecting Mounjaro straight from the refrigerator can cause the liquid to flow more slowly, creating a sensation of jamming. The pen should reach room temperature (30 minutes out of the fridge) before injection for optimal results.
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The needle is blocked or damaged. Using a needle more than once or accidentally touching the needle tip before injection can cause blockages. Each injection requires a fresh, sterile needle to ensure proper medication delivery.
Solutions:
Check you've removed both caps correctly and attached a new BD pen needle securely. The needle should click into place when properly fitted. Perform the safety check by dialling to the flow check symbol and pressing the injection button while pointing the pen upwards. You should see medication at the needle tip. If no medication appears, the pen may be genuinely faulty and should be replaced through your pharmacy.
Medication Leaking from the Pen
Observing liquid leaking from your Mounjaro pen understandably causes concern about whether you've received your full dose. Leakage usually manifests as droplets on the pen's exterior or medication pooling at the injection site.
Common causes:
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Removing the needle too quickly after injection. The MHRA guidelines for tirzepatide administration recommend keeping the pen pressed against your skin for at least five seconds after the injection button is fully depressed. This ensures complete medication delivery and prevents backflow.
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Reusing needles creates microscopic damage to the needle shaft, increasing leakage risk during subsequent attempts. The NHS explicitly advises against needle reuse for any injectable medication.
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Incorrect injection angle affects medication absorption and can cause surface pooling rather than proper subcutaneous delivery.
Solutions:
Count slowly to five after hearing the second click before withdrawing the pen from your skin. This simple step dramatically reduces leakage incidents. Always inject at a 90-degree angle into fatty tissue areas (abdomen, thigh, or upper arm). Pinch the skin gently before injection if you're particularly lean to ensure you're reaching subcutaneous fat rather than muscle.
Dose Counter Issues
The dose counter window should display your selected dose clearly before injection and show zero after successful administration. Sometimes the counter appears stuck, shows the wrong number, or fails to return to zero.
Troubleshooting steps:
Ensure you're turning the dose selector in the correct direction until it clicks at your prescribed dose. The pen won't allow you to select doses larger than what remains in the cartridge. If the counter won't turn to your prescribed dose, the pen may not contain sufficient medication for that dose.
After injection, the counter should show zero within 5-10 seconds. If it doesn't, you may not have pressed the injection button firmly enough or held it for sufficient time. Don't attempt to inject a second time with the same pen, as you may have received part of your dose. Contact Happy Pharmacy for guidance on whether you need a replacement pen.
Proper Storage: Preventing Problems Before They Start
Many Mounjaro pen issues stem from improper storage rather than device malfunction. The medication's effectiveness depends on maintaining proper storage conditions throughout its lifecycle.
Refrigeration Requirements
Unused Mounjaro pens must be stored in the refrigerator at 2-8°C, away from the freezer compartment. Freezing destroys tirzepatide's molecular structure, rendering the medication ineffective. Even briefly frozen pens should be discarded, regardless of whether they've thawed.
Store pens in their original carton to protect from light, which can degrade the active ingredient. Keep them in the main refrigerator compartment rather than the door, where temperature fluctuations occur with regular opening.
In-Use Storage Guidelines
Once you've started using a pen (removed the base cap and attached a needle), it can be stored at room temperature (below 30°C) for up to 21 days. This flexibility helps if you're travelling or don't have reliable refrigeration access.
Never store pens with needles attached. Remove and safely dispose of the needle after each injection to prevent contamination, air bubbles, and medication leakage. Recap the pen with its original cap between uses.
Travel Considerations
Travelling with Mounjaro requires planning to maintain proper storage. The medication can remain unrefrigerated during travel for up to 21 days, making short trips manageable without specialised cooling equipment.
For longer journeys, use medical-grade cool packs designed for injectable medications. Avoid direct contact between ice packs and pens, as freezing remains the primary storage risk. Many UK pharmacies stock travel cases specifically designed for weight loss injections.
Injection Technique: Maximising Safety and Results
Proper injection technique prevents most operational problems while ensuring you receive the full therapeutic benefit of your Mounjaro treatment.
Site Selection and Rotation
Rotate injection sites weekly to prevent lipohypertrophy (fatty lumps) that can affect absorption and cause discomfort. The abdomen offers the largest injection area and typically provides the most consistent absorption rates. Stay at least 5cm away from your navel and any scars.
The front and outer thighs provide alternative sites, particularly useful if you develop tenderness in your usual injection area. The back of your upper arm works but requires assistance or good flexibility to reach properly.
Preparation Steps for Trouble-Free Injections
Wash your hands thoroughly before handling the pen. Clean the injection site with an alcohol wipe and allow it to dry completely. Wet skin can cause stinging and may introduce bacteria.
Inspect the medication through the pen's viewing window. Mounjaro should appear clear and colourless. Cloudiness, particles, or discolouration indicate the medication has degraded and shouldn't be used.
Attach a new needle and perform the safety test before each injection. This removes air bubbles and confirms the pen is functioning correctly. You should see a small drop of medication at the needle tip after the safety check.
When to Contact Your Pharmacy
Despite troubleshooting efforts, some situations require professional guidance from a regulated online pharmacy like Happy Pharmacy.
If the pen is faulty you can also contact Eli Lilly directly to arrange for a replacement :
Phone : 01256 315 000 (press 1 after the automated intro)
Email : ukmedinfo@lilly.com
Contact us immediately if:
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Your pen appears damaged, cracked, or has been dropped from height. The internal mechanism may be compromised even without visible external damage.
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You suspect you've missed a dose due to pen malfunction. We can advise whether you should take a replacement dose or wait until your next scheduled injection.
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You experience unusual pain, excessive bleeding, or signs of infection at injection sites. While rare, these symptoms require prompt medical assessment.
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The medication appears discoloured or contains particles. Never use Mounjaro that doesn't meet visual inspection standards.
Why Choose Happy Pharmacy for Your Weight Loss Journey
As a fully regulated UK online pharmacy registered with the General Pharmaceutical Council, Happy Pharmacy provides more than just medication delivery. Our pharmacist-led service offers personal support throughout your weight loss treatment, ensuring you have access to expert guidance when troubleshooting issues arise.
Unlike unregulated sellers operating online, we guarantee genuine Mounjaro sourced directly from licensed UK wholesalers. Each prescription is reviewed by qualified pharmacists who can provide tailored advice for your specific circumstances.
Our commitment to patient safety means we're available to answer questions about injection technique, storage requirements, and troubleshooting whenever you need support. Trust in a regulated pharmacy provider ensures you receive authentic medication backed by professional expertise and a confidential online weight loss consultation.
Maintaining Treatment Consistency for Best Results
Successful weight loss with Mounjaro depends on consistent weekly dosing. Research published in The Lancet demonstrates that treatment adherence directly correlates with weight loss outcomes, with patients maintaining regular injection schedules achieving significantly better results than those with interrupted treatment.
When pen problems disrupt your routine, quick troubleshooting and access to replacement medication through a reliable online pharmacy like Happy Pharmacy keeps your treatment on track. Most injection pen issues resolve with simple adjustments to technique or storage practices.
Remember that your weight loss journey deserves the support of regulated healthcare professionals who prioritise your safety and success. Whether you're just starting Mounjaro or have been using weight loss injections for months, understanding how to troubleshoot common pen problems empowers you to take control of your treatment with confidence.
Blog medically reviewed by : Palvinder Deol, GPhC Registered Pharmacist, 24 January 2025
References:
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New England Journal of Medicine : Tirzepatide Once Weekly for the Treatment of Obesity
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Medicines and Healthcare products Regulatory Agency (MHRA). Mounjaro 2.5mg Solution for Injection in Pre-filled Pen: Summary of Product Characteristics.
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National Institute for Health and Care Excellence (NICE). Tirzepatide for treating obesity.
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