If you're using Mounjaro for type 2 diabetes or for off-label weight loss, you know how handy the Mounjaro injection pens are.
Each pen comes with 4 preset doses and is designed to be incredibly user-friendly-no need to see or handle the needle, no mixing required, and a preset dose to avoid any mistakes.
But, like with everything, there can still be malfunctions, and it's not uncommon for Mounjaro pens to be defective or not work as expected-like the pen not clicking properly or the lock button failing to unlock.
Don't panic! Here's a troubleshooting guide for your Mounjaro pen malfunctions and how to get a replacement.
Related article: Does Mounjaro Need to be Refrigerated? How to Store your Pens?
Just a quick note: Mounjaro pens are different in the UK and in the USA. They work differently. We're here talking about the USA model.
Common Mounjaro Pen Malfunctions
Mounjaro autoinjector pens are available in six different strengths (2.5 mg to 15 mg) to meet individual needs. Each pen contains four preset doses, and each box contains 4 pens, sufficient for a month's treatment.
To understand what can go wrong when using Mounjaro pens, here's a quick recap on how they work:
Photo Credits: @Eli Lilly
First, remove the pen cap. Then, place the pen against your skin. Unlock it by turning the lock button. Once unlocked, press the injection button until you hear two clicks, which signal the start and completion of the injection.
Related article: How to Inject Mounjaro and Use the Pen Injector Correctly?
What can go wrong with your Mounjaro Pen
While the Mounjaro pen is designed for simplicity and ease of use, like any medical device, it's not immune to occasional hiccups.
A few malfunctions can affect the pen and impact the delivery of medication. Here are some of the most common problems you might encounter with your Mounjaro pens:
- Misfiring pen. Occasionally, the pen may not release any medication when the injection button is pressed. This could be due to a mechanical failure within the pen or an issue with the medication cartridge.
- No clicking. The Mounjaro pen is supposed to produce an audible click when the dose starts and another one when it finishes. If you don't hear these clicks, it might indicate a malfunction, which can leave you unsure whether the full dose has been administered.
- Unlock button issues. Sometimes, you might find that the unlock button on your Mounjaro pen doesn't turn. This problem can prevent you from starting the injection process as the pen remains locked, even when you're ready to administer your dose. This issue could stem from a mechanical fault in the pen's design.
- Partial dose delivery. Sometimes, the pen may release only part of the dose. This can happen if the pen or the needle is blocked for example.
- Jammed pen. In some cases, the pen's mechanism itself may become jammed, preventing it from dispensing any medication at all. This can be caused by internal damage or debris that obstructs the pen's moving parts.
- Leaking medication. If you notice medication leaking from your Mounjaro pen either before or during an injection, this could be a sign of a malfunction or a crack in the pen's body.
How to Fix a Broken or Malfunctioning Mounjaro Pen
If your Mounjaro pen appears defective or malfunctions, do not attempt a DIY repair. Misguided attempts to fix the pen can lead to incorrect dosing and potential health risks.
Unfortunately, there's not much you can do yourself when faced with a malfunctioning Mounjaro pen. The proper steps include checking what can be wrong, attempting the injection one more time, and reporting the issue if it still does not work.
Troubleshooting Tips:
- Check the pen: Inspect your Mounjaro pen for any visible damage or medication leaks.
- Make sure it's unlocked. Mounjaro pens are locked for safety. Before injecting the medication, you must turn the lock button to unlock the pen. Make sure it's unlocked before injecting.
- Ensure it's well positioned. The clear base of the Mounjaro pen must be placed flat against your skin.
- Follow the instructions step by step: Always use the pen as directed by the manufacturer. Misuse can lead to malfunctions.
Related article: What are The Best and Worst Foods to Eat While on Mounjaro?
Never Break the Pen Open
It's come to our attention that some people might resort to a risky shortcut when faced with a malfunctioning Mounjaro pen: breaking it open to manually extract the medication with a syringe. This is not a safe practice.
The Mounjaro pen is precisely engineered to deliver the correct dosage. When you break it open, there's no way to ensure you're drawing the right amount of medication. This uncertainty can lead to serious health risks, including underdosing or overdosing.
Breaking the pen also compromises the sterility of the medication. This can expose you to infections, particularly if the syringe used to withdraw the medication isn't sterile. Besides, Tirzepatide, the medication in Mounjaro pens is sensitive to environmental conditions. Exposing it to air and uncontrolled temperatures by breaking the pen could degrade its effectiveness.
If your Mounjaro pen isn't working, the safest option is to contact your healthcare provider for advice or get a replacement pen from the pharmacy or the manufacturer. Never take risks with your health by trying to DIY a solution that could end up doing more harm than good.
Remember, safety first! It's always better to wait for a proper replacement than to risk an improper dose or infection by attempting to extract the medication yourself.
Related article: How to Travel with Mounjaro: Safety Tips & Travel Cases.
Defective Mounjaro Pen Replacement by Eli Lilly
If you need a replacement for a defective Mounjaro pen, the manufacturer Eli Lilly may provide support.
Contact their customer service at the provided phone number for assistance in the USA: 1-833-807-MJRO (833-807-6576). Make sure to have accurate records of your pen's lot number and the issue encountered for a smoother replacement process.
Related article: What to Do If You Accidentally Leave Mounjaro Out of the Fridge.
Mounjaro Pen Malfunctions: FAQs
How do I know if I injected Mounjaro correctly?
A successful injection is typically confirmed by hearing two clicks-the first indicates the start, and the second confirms the completion of the injection.
Ensure you hear these 2 clicks and wait for at least 10 seconds while pressing the injection button. Another sign that you've injected Mounjaro correctly is when you see the grey plunger inside the pen. It's not visible before the injection, but only once the medicine has been administered.
Related article: What Happens if Mounjaro Gets Warm?
What if the Mounjaro pen only clicked once?
If the pen only clicked once, it might not have delivered the full dose. Consult your healthcare provider or pharmacist for advice on how to proceed.
Is there a reset button on the Mounjaro pen?
No, the Mounjaro pen does not feature a reset button. If your pen is not functioning correctly, it should be replaced.
I did not feel the Mounjaro injection. Is that normal?
It is possible not to feel the injection due to the pen's design to minimize pain and discomfort. If you heard the 2 clicks and can see the grey plunger, the injection has been completed, even if you did not feel it.
Related article: When to Take Mounjaro: Should You Take it in The Morning or at Night?
We'd Love to Hear From You!
Do you have questions or experiences with Mounjaro pen malfunctions? Have you ever had to get a replacement from the manufacturer? Share your stories and questions in the comments below. Your insights could help others too!
Comments
4AllFamily Customer Service said:
Hi Tammy,
We’re so sorry to hear what you’ve been going through—that sounds incredibly frustrating and concerning, especially when you’ve been using Mounjaro without issues until now. You’re absolutely right to stop using the remaining pens if you’re unsure of their reliability.
Unfortunately, since we’re not the manufacturer or pharmacy, we can’t directly replace pens or access your prescription records. However, you’re not alone—this kind of malfunction has been reported by others too, and Eli Lilly (the manufacturer) should definitely be made aware.
We recommend trying to reach them through their Mounjaro Patient Support contact page or calling 1-800-LILLY-RX (1-800-545-5979) during business hours and selecting the option for product complaints. If you’re still unable to reach them, consider asking your doctor’s office or pharmacist to escalate the issue on your behalf—they often have direct contacts with pharmaceutical reps.
We really hope you get the support you need and that this is resolved quickly.
—The 4AllFamily Team
4AllFamily Customer Service said:
Hi Tina,
Thanks for sharing your experience—you’re definitely not alone. We’ve heard from several users who’ve had similar issues with the second click not happening during injection. It can be really concerning, especially when you’re following all the instructions correctly.
The second click is supposed to confirm that the injection is complete, but if it doesn’t happen—even after holding the button down for over 10 seconds—it could indicate a malfunction. We recommend contacting the manufacturer, Eli Lilly, directly to report the issue. They may be able to provide a replacement and investigate the problem further.
You’re doing everything right by checking and reaching out. We hope you get a quick resolution!
—The 4AllFamily Team
4AllFamily Customer Service said:
Hi Michelle,
We’re really sorry to hear about your experience—how frustrating that must be, especially given the cost of Mounjaro pens. While we don’t manufacture the medication or devices, we totally understand your concern and you’re not alone—several users have reported similar issues.
If the pen won’t advance or dispense the medication properly even after replacing the needle, we strongly recommend reaching out directly to the manufacturer, Eli Lilly. They may be able to replace faulty pens or offer guidance on what to do next. Your pharmacy might also be able to assist or escalate the issue.
We hope you’re able to get a resolution soon—no one should have to waste such an important (and expensive) treatment.
Take care,
—The 4AllFamily Team
4AllFamily Customer Service said:
Hi Michael,
Thanks for your comment! We’re not medical professionals, so we always recommend checking with your healthcare provider or pharmacist to be sure. That said, it’s normal for the Mounjaro pen to still contain medication even if it’s not clearly visible in the glass window. As long as you hear the click and follow the instructions for use, the dose should be delivered properly.
If you’re ever unsure whether the pen is working or if the dose is being administered correctly, your doctor or pharmacist can walk you through a test dose or check the pen with you. You’re not alone—this is a common concern for many users.
Take care, and feel free to reach out if you have more questions!
—The 4AllFamily Team
Michael said:
I have a 15mg quick pen injecting 2.5mg to make it last. I can’t see liquid in the glass when I load it so I don’t know if it’s working or not. Any help would be appreciated
Tina Cochrane said:
just had 2 pens now not do 2nd click . I thought maybe something wrong I’m holding button down over min nothing I chk internet see if this is me doin wrong no is seems be big problem.
Tammy Harrison said:
I have used Mounjoro for several months with no problems. I recently obtained a new pack of four pens and two of the four did not work as usual. The first one did not “click” at all and when I removed it from my abdomen, the contents sprayed on top of my foot. I used a second one just so that I can remain in schedule and it did the same thing, only it sprayed in the air. I received none of the medication either time. I contacted the pharmacy where I obtained the prescription and I was told to contact the manufacturer because there is nothing they could do
I have called your company three times since 05/04/25 and cannot get passed the automated system. I am already off schedule now and I am pen pens short for this month. Please advise how I can have the two pens replaced. I don’t want to try the remaining two from this prescription. Thank you
Michelle Commerford said:
This is the second monjaro pen that has no budged and impossible to wid out. This is too expensive to just throw away and from what I read and the amount of people having issues with these pens yet there is zero accountability taken. I have been using these pens for 5 months now and am not doing anything different I have attached a nother needle making sure it is straight still unable to wind the damned thing out it won’t budge.
4AllFamily Customer Care Team said:
Hi Janine, thanks for your comment. We’re sorry to hear your Mounjaro pens malfunctioned. If the medicine was squirting and the second click didn’t happen, the pens may be defective. We recommend contacting your pharmacist or the manufacturer (Eli Lilly) as soon as possible—they can assist with a replacement and report the issue.
4AllFamily
Janine Zimmerman said:
I have 2 of my Mounjaro shots that have malfunctioned and medicine was squirting everywhere. It did not click on the 2nd click.
4AllFamily Customer Care Team said:
Hi Tim,
Thank you for sharing your experience with us. We’re sorry to hear about the malfunctions you’ve encountered with your Mounjaro pens. This is certainly unusual, and we had not previously heard of this specific issue. It might be helpful to report these incidents to the manufacturer or your pharmacy. They can provide guidance and potentially replace the malfunctioning pens to ensure you can continue your treatment without further issues. Documenting such malfunctions helps improve product quality and user safety.
Best regards,
4AllFamily
4AllFamily Customer Care Team said:
Hi Brenda,
I’m sorry to hear about the issue you experienced with your Mounjaro pen. Unfortunately, as we are not the manufacturer, we are unable to provide replacements. I recommend contacting the manufacturer’s customer service or your pharmacy as soon as possible to report this malfunction and inquire about getting a replacement for your Mounjaro pen. They should be able to assist you in ensuring you have the medication you need for your next dose.
Best regards,
4AllFamily
Brenda said:
I have been taking my shot and my stomach and I decided to switch to my thigh and when I went to take the shot it misfunctioned and the medication went squirting everywhere. I would like to find out if you will do replacements? I was supposed to take another shot and I’m not going to have enough now.
Tim Black said:
I have had two malfunctions that are not listed here. When removing the cap and preparing for an injection, the mechanical part of the pen came off with the cap. That injection didn’t work, so I tried my other and final injection. The same thing happened again. In both cases, I tried to repair the pens, but I couldn’t get the broken part out of the cap. I could have used pliers, but that would destroy the part. I have been using Mounjaro for many months, and this is the first time it has malfunctioned…twice.
4AllFamily said:
Hi Teena,
We’re really sorry to hear about your frustrating experience with the Mounjaro injectors. That sounds incredibly stressful, especially when dealing with a medication you rely on.
If you’re experiencing repeated issues with multiple injectors, it might be helpful to check in with your doctor or a nurse to ensure everything is being administered correctly. Sometimes, injection technique can make a difference, and a healthcare professional could provide guidance to help avoid wasted doses.
That said, it’s disappointing to hear about the difficulties with replacements. We understand how important every dose is, and we hope Eli Lilly can provide a better resolution for situations like this in the future. In the meantime, you might also want to check with your pharmacist or insurance provider to see if they have any suggestions for addressing this issue.
Wishing you the best, and we hope everything gets sorted out soon!
4AllFamily Customer Care Team
Teena Selzer said:
I have experienced defective Mounjaro injectors twice now. In January, 2025 I attempted to take my weekly dose and ended up going thru 4 injectors (same box) before the 5th injector pen worked properly. I contacted Eli Lilly and they replaced the box. A month later, the same thing happened. This time I had to go thru 8 injectors (all the same lot number) before the 9th one worked. I contacted Eli Lilly again and they indicated that they will replace 1 box of injectors but refused to place the 2nd box since they replaced a box in January. A reputable company like Eli Lilly is refusing to back their defective injectors. I am a senior citizen living on a limited income. Every penny I spend counts. Besides that, how am I supposed to go without 1 month of medication? I spoke to one of their Reps today who informed me of their decision. When I asked her that same questions she said that some medications stay in your body for a month. I was surprised that she was indicating it would be alright to go without the medicine for that period of time. What will I do if this happens again? Eli Lilly does not stand behind their products.
4AllFamily Customer Care Team said:
Dear Jennifer,
Thank you for reaching out and sharing your concerns regarding your Mounjaro pen. We understand the frustration and distress caused by the lack of response you’ve experienced.
However, we would like to clarify that our blog is an independent platform and is not affiliated with the manufacturer of Mounjaro.
For assistance with your Mounjaro pen, we recommend contacting the manufacturer’s customer support directly. You can reach them at:
Lilly Support Service at 1-800-LillyRx (1-800-545-5979)
MOUNJARO.LILLY.COM
We hope this information helps you resolve the issue promptly. If you have any other questions or need further assistance, please feel free to reach out.
Best regards,
4AllFamily
Jennifer said:
My pen will not release the next does. The pharmacists looked at it and lodged a fault notice with your company about two weeks ago now. I have provided all my contact information. No one has contacted me. I have called the number myself to lodge fault and again have left my name and email.
Again no response from your company regarding faulty pen. Please reply to your customers as this medication is expensive and when the pen is faulty this costs me money, time and distress. Please respond to me.