If your Mounjaro pen is stuck, jammed or not working, there are several possible reasons. The needle may be missing, bent, damaged or blocked. The KwikPen may have already delivered all four doses, it may have been primed more than necessary, or there may be a genuine device fault.
There is no reset button on a Mounjaro KwikPen, and forcing the dose knob will not fix a mechanical problem.
That matters because using the wrong fix could damage the device, waste medication or result in an incomplete injection. Advice online can also be confusing because some injection pens work differently from the Mounjaro KwikPen. The KwikPen has fixed doses and does not use a numbered dose scale.
Whether you searched for my Mounjaro pen is stuck, my Mounjaro pen has jammed, my KwikPen is stuck, my Mounjaro pen is not working or simply Mounjaro pen stuck, this guide is for UK Mounjaro users using the KwikPen. It explains what different problems can mean, what the manufacturer advises, when you should stop using the pen, what to do if a dose is incomplete, and how to report a suspected defective or falsified pen.
Key Things to Know
- The KwikPen contains 4 fixed doses of 0.6 ml. It also contains extra solution used for priming.
- If the dose knob is difficult to push, the needle may be missing, bent, damaged or blocked.
- A Mounjaro pen stuck on the last dose may simply have reached the end of its 4 dose supply. Do not try to extract the remaining solution.
- There is no Mounjaro pen malfunction reset button. If the pen does not work normally after following the manufacturer's instructions, do not try to repair it yourself.
- If a pen stops working during an injection and you are unsure how much medicine was delivered, do not take another dose to make up the difference. Contact your prescriber or pharmacy for advice.
Start Here: What a Stuck Mounjaro Pen Usually Means
Search terms such as Mounjaro pen jammed UK, jammed Mounjaro pens, Mounjaro KwikPen jammed, Mounjaro pen locked, Mounjaro pen blocked and Mounjaro injection stuck can all describe different problems.
The safest approach is to work out what the pen is doing before trying anything. Do not use force if the dose knob will not move.
| What you are seeing | Possible explanation | What to do |
|---|---|---|
| Dose knob is hard to push | The needle may be blocked, damaged or incorrectly attached | Follow the manufacturer's needle and priming instructions. If the problem continues, do not force the knob |
| Dose knob will not turn | The pen may have delivered all 4 doses, or there may be a device problem | Check how many doses have been given. Do not force the knob |
| Mounjaro pen stuck on last dose | The pen may have reached the end of its 4 dose supply | Do not try to obtain another dose from the remaining solution |
| Mounjaro pen jammed after 3 doses or stuck before the fourth dose | The pen may have been primed more than required, or there may be another device problem | Do not try to extract the remaining medicine. Contact your pharmacy or prescriber |
| Mounjaro needle stuck on pen | The needle may not have been removed correctly | Follow the Instructions for Use. Never grip a bare needle with your fingers or use tools such as pliers |
| Mounjaro pen not priming | The needle may be blocked or the pen may not be functioning correctly | Follow the manufacturer's priming instructions. If medicine still does not appear after the permitted priming attempts, contact the manufacturer or your healthcare professional |
| Cracks, leaks or visible damage | The pen may be defective or damaged | Do not use it. Keep the pen and packaging and contact your pharmacy |
| Dose knob comes away from the pen | This can be a sign of a defective or falsified pen | Do not use it or try to extract the dose. Keep the pen and packaging and report it |
Working out which situation you are dealing with is more useful than simply trying to push the knob harder. If a pen does not behave as described in the manufacturer's instructions, stop and ask your pharmacy or prescriber for advice.
How the Mounjaro KwikPen Is Actually Built
Mounjaro is supplied in the UK as the KwikPen, a pre filled, multi dose device. Each pen contains 2.4 ml of solution, providing 4 fixed doses of 0.6 ml. There is additional solution to allow the pen to be primed before injections.
The different strengths contain different concentrations of tirzepatide. The volume delivered for each fixed dose remains 0.6 ml.
The KwikPen does not have a numbered dose scale like some other injection pens. The dose window and dose knob are used to prepare and deliver the fixed dose. The manufacturer's Instructions for Use explain how to prime the pen before each injection and how to confirm that the injection has been completed.
The pen is designed to deliver 4 weekly doses. Medication remaining after those doses does not mean that another complete dose is available. The manufacturer's instructions say to dispose of the pen after 4 weekly doses.
There Is No Mounjaro Pen Malfunction Reset Button
Searches for a Mounjaro pen malfunction reset button are common, but the KwikPen does not have a reset switch or repair function.
If you have a problem during priming, the manufacturer's instructions provide a limited sequence of steps involving the pen needle and priming process. These steps should be followed exactly as supplied with your pen.
If the pen still does not work correctly after following those instructions, do not try to dismantle it, repair it or force the dose knob. Contact your local pharmacy, prescriber or the manufacturer for advice.
Why a Mounjaro Pen Is Hard to Push
If a Mounjaro pen is hard to push, check the needle and follow the manufacturer's instructions before assuming the pen itself is faulty.
- Prime the pen before each injection as described in the Instructions for Use.
- Use a new compatible needle for each injection.
- Check that the needle is correctly attached and is not bent or damaged.
- If the dose knob is difficult to press, do not use extra force.
- Never try to inject without a needle attached.
- Do not store the pen with the needle attached, as this can increase the risk of leaking, blocking the needle or allowing air to enter the pen.
The manufacturer's instructions allow limited repeat priming if no medicine appears at the needle tip. If medicine still does not appear after the specified steps, the instructions advise contacting the local Lilly affiliate.
If the pen remains difficult to use, do not keep trying to force it. Ask your pharmacy or prescriber what to do next.
Storage Is an Important Part of Pen Care
Correct storage helps protect the medicine and the pen. Unused Mounjaro KwikPens should be stored in a refrigerator between 2°C and 8°C. They must not be frozen.
After first use, the KwikPen can be stored at room temperature up to 30°C and should be discarded 30 days after first use or after 4 weekly doses, whichever applies first according to the product instructions. The pen should be kept away from heat and stored with its cap on.
Do not store the pen with a needle attached. This can cause leaking, blocking or air entering the pen.
If the pen has been frozen, do not use it. It should be discarded. Do not try to warm a frozen pen and use it afterwards.
Mounjaro Pen Stuck on Last Dose
A Mounjaro pen stuck on the last dose does not necessarily mean that the pen is broken.
Each KwikPen is designed to provide 4 weekly doses. After those doses have been given, some solution can remain in the pen because additional solution is included for priming.
Do not treat the remaining solution as a fifth dose. The pen should be disposed of after the 4 weekly doses as instructed by the manufacturer.
So, if your search was Mounjaro last dose stuck or Mounjaro pen jammed on last dose, first count how many injections you have already taken from that pen. If you have received 4 doses, do not try to force out any remaining medicine.
Mounjaro Pen Jammed After 3 Doses or Stuck on 4th Dose
If a pen will not deliver the fourth dose, there are several possible explanations. One possibility is that the pen has been primed more than required, which can use some of the additional solution intended for priming.
The manufacturer's instructions are important here. Do not try to extract the remaining medicine from the pen or use another method to obtain a dose.
If your pen has stopped working before you have received the expected 4 doses, contact your pharmacy or prescriber. Keep the pen and packaging because the batch number and other details may be needed when investigating a suspected device problem.
If the same problem happens repeatedly, tell your pharmacy. They can help determine whether the problem is related to how the pen was used or whether the device needs to be reported as a possible defect.
Mounjaro Pen Not Twisting, Not Clicking or Not Priming
When a Mounjaro pen will not turn, the first step is to check the dose window and how many doses you have already taken. Do not rely only on whether you can hear a click.
If a Mounjaro pen is not priming and no medicine appears at the needle tip, follow the manufacturer's priming instructions. The current Instructions for Use state that if no medicine appears, priming can be repeated a limited number of times. If medicine still does not appear after the specified steps and a needle change, contact the local Lilly affiliate.
A Mounjaro pen not clicking does not automatically mean that it is broken. However, if the pen will not operate as described in the Instructions for Use, do not force it.
Whether your Mounjaro pen will not twist, feels locked or appears stuck, the safest option is to stop and seek advice rather than trying to repair the mechanism yourself.
Needle Stuck on Mounjaro Pen, or Needle Not Going In
Searches for needle stuck on Mounjaro pen or a Mounjaro needle stuck on pen after injecting can describe several different situations.
Mounjaro KwikPens are used with compatible pen needles, which are supplied separately. A new needle should be used for every injection.
If a needle becomes stuck, follow the Instructions for Use for removing it safely. The outer needle shield is designed to help with this process. Never grip a bare needle with your fingers and do not use pliers or other tools.
If a needle looks bent, damaged or blocked, replace it with a new compatible needle. Do not try to straighten or unblock a used needle.
The manufacturer's instructions also state that the pen should not be stored with the needle attached because this can cause leaking, needle blockage or air entering the pen.
If the Pen Jams Part Way Through an Injection
A Mounjaro injection that stops part way through can be worrying. The important thing is not to guess how much medicine you received.
The manufacturer's Instructions for Use explain how to hold the dose knob down during the injection and how to check the dose window afterwards. If you are unsure whether the full dose was delivered, do not take another dose to compensate.
Do not re dial the pen, try to extract medicine or use a second pen to make up what you think may be missing. Taking another dose could result in more medicine than intended.
Instead, keep the pen and contact your prescriber or pharmacy as soon as possible. Tell them what happened and, if you can, explain what the dose window showed and whether any medicine appeared at the needle tip.
Faulty, Damaged or Frozen Pens, and How to Report Them
People often use terms such as Mounjaro pen broken, broken Mounjaro pen and Mounjaro faulty pen to describe any pen that does not work normally. A device that has reached the end of its 4 doses is different from a pen that is physically damaged or potentially falsified.
Check the pen before use and do not use it if there is visible damage or if the medicine does not look as expected.
| Warning sign | What it may suggest | Action |
|---|---|---|
| Visible cracks or physical damage | The device may be damaged | Do not use the pen |
| Leaking solution | The device may not be intact | Do not use the pen and contact your pharmacy |
| Solution is not clear | The medicine may not be suitable for use | Do not use the pen and seek advice |
| Pen has been frozen | The medicine may have been damaged by freezing | Do not use the pen |
| Dose knob comes away from the pen body | Possible device fault or falsified pen | Do not use it. Keep the pen and packaging and report it |
| Needle is visibly bent or damaged | Needle problem | Replace the needle |
| Pen exposed to contamination such as dirt or liquid | The device may not be suitable for use | Do not try to clean and reuse it |
One warning deserves particular attention. In February 2026, the MHRA issued an alert about falsified Mounjaro KwikPen 15 mg pens with batch number D873576. The affected pens had been supplied through one UK online pharmacy, and several had a dose knob that came off during use. The MHRA advised patients with an affected pen not to use it and not to try to extract any dose.
The MHRA also confirmed that D873576 is a legitimate batch number for genuine 7.5 mg Mounjaro KwikPens, so the alert applies specifically to 15 mg pens with that batch number.
If you have a 15 mg pen with batch number D873576, do not use it. Keep the pen in a safe place and follow the MHRA reporting advice. If you are unsure whether your pen is affected, speak to a healthcare professional.
Temperature also matters. Unused Mounjaro KwikPens should be stored at 2°C to 8°C and must not be frozen. After first use, the pen may be stored at room temperature up to 30°C according to the current product instructions.
Suspected defective or falsified medicines can be reported through the MHRA Yellow Card scheme.
What a Stuck Pen Means for Your Dose Timing
A device problem can create a second concern: when should you take your next dose?
If a Mounjaro dose is missed, the current UK product information says it should be taken as soon as possible within 4 days. If more than 4 days have passed, the missed dose should be skipped and the next dose taken on the usual day. You should not take 2 doses within 3 days of each other.
If your pen has failed and you are unsure when or how to take your next dose, contact your prescriber or pharmacy rather than changing your treatment schedule yourself.
Wider guidance on weight management treatment is available in our weight loss treatment options.
When Mounjaro Is Not Working and the Pen Is Fine
Not every search for Mounjaro pen not working or Mounjaro injection not working is actually a device problem.
Some people mean that their pen is working normally but they feel that the effects of treatment have changed. If the pen operates as described in the Instructions for Use and the dose is delivered correctly, a change in appetite or weight loss should be discussed with your prescriber rather than treated as a pen malfunction.
Do not change how much you inject, inject more often or try to obtain additional medicine from the pen because you feel that treatment is less effective.
Storage should still be checked. A pen that has been frozen should not be used, and the storage instructions should be followed carefully to help protect the medicine.
Preventing Jams and Getting a Replacement
- Use a new compatible needle for every injection and remove it after use.
- Prime the pen according to the manufacturer's Instructions for Use. Do not repeatedly prime it unnecessarily.
- Keep the pen capped when it is not being used and follow the recommended storage conditions.
- Check the pen before use for visible damage, leaks or other problems.
- Keep the pen and packaging if you think the device is faulty. The batch number may be important when reporting a problem.
- Keep track of your 4 weekly doses so you know when the pen has reached the end of its intended use.
If the pen appears faulty, contact the pharmacy that supplied it rather than trying to repair the device yourself. Keep the pen, packaging and batch number if possible.
Your pharmacy or prescriber can advise you about the next dose and whether a replacement pen is needed. A UK registered pharmacy can also help with reporting a suspected defective product to the manufacturer.
If you are considering Mounjaro or want more information about treatment, you can read our Mounjaro weight loss treatment page.
Medical Disclaimer
This page provides general information about the Mounjaro KwikPen. It is not medical advice, a diagnosis or a substitute for the Instructions for Use and Patient Information Leaflet supplied with your medicine.
Mounjaro is a prescription only medicine and should only be used under the supervision of an appropriately qualified prescriber. Treatment suitability depends on an individual clinical assessment, and results vary between individuals.
The device information in this guide is intended to help you understand common problems with a Mounjaro KwikPen. It does not replace the manufacturer's instructions. Do not dismantle, repair or modify the pen, and do not try to extract medicine from a defective or empty pen.
If you think your pen is faulty, contact your pharmacy or prescriber. If you have a 15 mg Mounjaro KwikPen with batch number D873576, do not use it and follow the MHRA advice.
Suspected side effects, defective products and falsified medicines can be reported through the MHRA Yellow Card scheme. If you feel seriously unwell after using Mounjaro, seek urgent medical attention. In an emergency, call 999.