If you are holding a Mounjaro pen that will not deliver a dose, this guide is for you. It is also for people who have already taken their fourth injection, can still see liquid in the pen and are wondering whether they can use it.
These are two different situations, and they need different answers.
Here is the short version. A Mounjaro KwikPen contains four fixed doses. The fourth dose is your final prescribed dose from that pen. If liquid remains after the fourth injection, the manufacturer's patient information says not to use it.
The rest of this guide explains what to do in each situation and answers some of the common questions people have about the last dose of a Mounjaro pen. It is written for UK patients and is based on current UK product information.
Key Takeaways
- A Mounjaro KwikPen contains four doses of 0.6 ml, with one dose taken once a week.
- Your fourth dose is the last labelled dose in the pen. If the pen will not deliver it correctly, stop and contact your dispensing pharmacy.
- Liquid may remain after the fourth dose. The patient information leaflet says not to use any medicine left in the pen.
- The remaining liquid should not be treated as an additional dose because the amount is not intended to be measured or administered as another dose.
- The KwikPen provides fixed doses. Do not try to count clicks or use the device to create a smaller dose.
- Never force, dismantle or modify the pen. Contact your dispensing pharmacy if something does not seem right.
- Tirzepatide has a half life of approximately 5 days, so it remains in the body for some time after a dose.
- Whether Mounjaro is suitable for you depends on your individual clinical assessment. Results and side effects can vary between people.
What "Last Dose" Actually Means: Four Different Situations
Before trying to troubleshoot your pen, it helps to understand what is happening. The right action depends on the situation.
| Situation | What you are looking at | Is it a labelled dose? | What to do |
|---|---|---|---|
| Dose four will not deliver | The pen has not delivered the fourth dose correctly or the mechanism will not work | Yes, this is your prescribed dose | Stop, do not force it, contact your pharmacy |
| Liquid left after dose four | Four doses have been correctly given, but some solution is still visible | No, it is not an additional labelled dose | Do not use the remaining medicine and discard the pen as instructed |
| You want a smaller dose than the pen gives | You want to take less than the strength prescribed for the pen | No, the pen is not designed for this | Speak to your prescriber about your prescribed strength |
| You want the medicine out of your body | You are experiencing side effects or want to stop treatment | This is not a pen problem | Speak to your prescriber or pharmacist |
The important point is this: if all four doses have been correctly given, do not use the remaining liquid simply because you can still see it in the pen. The UK patient leaflet specifically says that a small amount may remain and should not be used.
How Many Doses Are in a Mounjaro Pen?
Each Mounjaro KwikPen is a multiple dose, pre filled pen designed to deliver four weekly doses. Each dose is 0.6 ml.
The current UK Summary of Product Characteristics states that each KwikPen contains four doses of 0.6 ml that can be administered. The patient information leaflet also confirms that each pen contains four doses of Mounjaro in one of the available strengths: 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg or 15 mg.
The Mounjaro KwikPen received its first UK marketing authorisation on 25 January 2024.
If you are looking for information about the last dose, remember that the pen is designed to provide four doses. Any liquid remaining after those doses should not be treated as a fifth dose.
Follow the prescribed dosing schedule and the Instructions for Use supplied with your pen. If you are unsure whether you received your full dose, contact your prescriber or dispensing pharmacy rather than trying to use the remaining liquid.
| Specification | Detail |
|---|---|
| Doses per pen | 4 |
| Volume per dose | 0.6 ml |
| Total volume of four labelled doses | 2.4 ml |
| How long one pen lasts | 4 weeks, one injection per week |
| Available strengths | 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, 15 mg |
| Doses per month | 4 |
| Can it deliver a partial dose? | No |
The strength changes between pens. The number of fixed doses does not.
Mounjaro Last Dose Stuck: What Is Actually Going On
If you have not successfully given your fourth dose and the pen is not working as expected, do not assume that the remaining liquid is an extra dose.
Your fourth dose is part of your prescribed treatment, so a problem with the pen should be dealt with rather than worked around.
Do not force the mechanism or try to open the pen. Contact your dispensing pharmacy if the pen appears damaged, does not work as expected or you are unsure whether you received the full dose.
Common reasons a Mounjaro pen may not deliver as expected
| Possible issue | What you may notice | What to do |
|---|---|---|
| Pen is cold from the fridge | The pen may feel different to handle | Follow the storage and use instructions supplied with your pen |
| Needle is not attached correctly | No medicine comes out or there is leakage | Check the needle and follow the Instructions for Use |
| Needle is blocked or damaged | Little or no medicine comes out | Use a new compatible needle as instructed |
| Dose counter does not advance | The expected dose is not showing | Stop and contact your pharmacy rather than repeating the injection |
| Priming issue | Medicine does not appear during priming | Follow the priming instructions supplied with your pen |
| Pen appears damaged | Cracks, leakage or another visible problem | Stop using it, keep the pen and packaging, and contact your pharmacy |
What not to do
- Do not force the injection mechanism.
- Do not dismantle the pen or try to open the cartridge.
- Do not transfer the solution into a syringe.
- Do not repeat the priming steps more than instructed in the Instructions for Use.
- Do not skip or double your next injection to compensate for a dose you think may have been incomplete. Speak to your prescriber first.
- Do not use leftover liquid after the four labelled doses have been given.
Follow the Instructions for Use that came with your pen. If you are unsure about any step, ask your pharmacist or prescriber before injecting.
Can You Use the Last Bit of Mounjaro Left in the Pen?
This is one of the most common questions about Mounjaro pens.
The answer is no. The current UK patient information leaflet states:
"A small amount of medicine may remain in the pen after all doses have been correctly given. Do not try to use any remaining medicine."
It also states that after the last dose has been given, the pen must be properly discarded.
This means that seeing liquid in the pen after your fourth injection does not mean you have another dose available.
Why is there liquid left after the fourth dose?
The official UK product information confirms that some excess solution may remain in the pen after use. It does not describe this remaining liquid as a fifth dose and does not give patients a method for measuring or using it.
There can be several practical reasons why some solution remains in a pre filled injection device, including the way the pen delivers the medicine and the small amounts of solution that can remain within the delivery system.
However, the exact amount left can vary. For this reason, you should not try to estimate a dose from the amount you can see.
The safest approach is simple: once the four labelled doses have been given, do not try to use the remaining liquid. Follow the manufacturer's disposal instructions.
Why the residue cannot be treated as a dose
The important point is that any liquid left after the four labelled doses is not a measured dose. The amount can vary, so there is no reliable way to know how much tirzepatide it contains or how much you would actually receive.
Trying to remove the remaining liquid can also involve handling the pen in a way that is not covered by the manufacturer's instructions. This could affect the device or introduce contamination.
If you are asking because of the cost of treatment or a gap in your supply, speak to your prescriber or dispensing pharmacy. They can help you decide what to do without changing your treatment yourself.
Priming Waste: Why Some Pens May Run Short Before Dose Four
This section is important because correct priming and injection technique can help you avoid unnecessary medicine loss.
Priming, also called a flow check, is part of preparing the KwikPen for injection. Follow the Instructions for Use supplied with your pen and only repeat the priming steps when the instructions tell you to do so.
If the pen does not appear to be priming correctly, do not keep repeating the process unnecessarily. The current Instructions for Use gives specific steps to follow if no medicine appears. If the problem continues, contact your pharmacy or healthcare professional.
It is not possible to say that repeated priming is the reason every pen that does not deliver a fourth dose has run short. A problem with the pen, needle or injection process can have other causes.
What a wasted dose actually costs
| Strength | Standard price per pen | Cost per weekly dose | Value lost if one dose is wasted |
|---|---|---|---|
| 2.5 mg | £174.99 | £43.75 | £43.75 |
| 5 mg | £204.99 | £51.25 | £51.25 |
| 7.5 mg | £254.99 | £63.75 | £63.75 |
| 10 mg | £274.99 | £68.75 | £68.75 |
| 12.5 mg | £304.99 | £76.25 | £76.25 |
| 15 mg | £323.99 | £81.00 | £81.00 |
Standard list prices as displayed on the EveryDayMeds Mounjaro product page. Prices are subject to change and exclude any promotional offer.
Following the Instructions for Use carefully, using a new compatible needle for each injection and avoiding unnecessary repeat priming can help reduce avoidable medicine loss. If your pen does not appear to deliver a dose correctly, contact your dispensing pharmacy rather than trying to recover medicine from the pen.
Can You Get 2.5 mg Out of a 5 mg or 7.5 mg Mounjaro Pen?
No. The Mounjaro KwikPen is designed to deliver four fixed doses of 0.6 ml at the strength shown on the label. It is not designed to measure or deliver a smaller dose.
People sometimes ask how many "clicks" correspond to a lower dose. There is no approved click to dose conversion for the KwikPen. The dose window and the Instructions for Use should be used rather than counting clicks.
Trying to take a smaller amount by removing the medicine with a separate syringe is not covered by the manufacturer's instructions. It can also make the amount of medicine you receive difficult to measure accurately.
What to do instead
There can be different reasons why someone may want a lower dose. For example, you may be having side effects, dealing with a supply issue or finding the cost difficult to manage. These are situations to discuss with your prescriber.
- Struggling with side effects? Your prescriber can decide whether a dose increase is appropriate or whether you should remain on your current strength for longer.
- Worried about cost? Ask your prescriber or pharmacy about your treatment options. The most suitable strength should be based on your clinical needs, not simply on the price of the pen.
- Facing a supply gap? Speak to your pharmacy or prescriber before changing your injection schedule or trying to make a pen last longer.
Your prescriber will determine the appropriate strength and dosing schedule for you. Do not try to change the dose yourself.
How Long Does Mounjaro Stay in Your System?
This is a different question from how the pen works, but it often comes up when people are thinking about stopping treatment or are concerned about side effects.
The Summary of Product Characteristics states that tirzepatide has a half life of approximately 5 days. This means the amount of tirzepatide in the body decreases gradually over time rather than disappearing immediately.
In practical terms, tirzepatide can remain in the body for several weeks after the final injection. The approximately 5 day half life is also one of the reasons Mounjaro is given once a week.
There is no recommended method for quickly removing tirzepatide from the body. If you are stopping treatment or experiencing side effects, speak to your prescriber rather than trying to speed up the process yourself.
If you think you have taken more Mounjaro than prescribed, contact your prescriber, pharmacist or NHS 111 for advice. The UK product information states that there is no specific antidote for an overdose and that treatment is based on the symptoms, with a prolonged period of observation potentially needed because of tirzepatide's half life.
Injecting Your Final Dose: Sites and Aftercare
The Instructions for Use supplied with your Mounjaro KwikPen should always be your main guide for using the pen. The information below explains the key points but does not replace the manufacturer's instructions.
Recommended Injection Sites for Mounjaro
Mounjaro is injected under the skin into the abdomen, thigh or back of the upper arm. If the back of the upper arm is used, another person should give the injection.
The product information also recommends rotating injection sites with each dose.
Importance of Rotating Injection Sites
Try not to inject into exactly the same spot each time. Rotating the injection site can help reduce repeated irritation to one area.
You can use the same general body area for your weekly injection, but choose a different spot within that area. If you also use insulin, use a different injection site for Mounjaro.
Keeping a simple note of where you last injected can make it easier to remember which areas you have used.
Normal Reactions After Injection
A small drop of blood after removing the needle can happen. The current Instructions for Use advises lightly pressing the area with gauze or a cotton ball if this happens and not rubbing the injection site.
You may also notice some mild redness or tenderness around the injection site. If you are concerned about a reaction or it does not settle, speak to your pharmacist or prescriber.
A small drop of medicine on the needle tip after an injection can also be normal and does not mean that you need to take another dose.
Signs That Need Checking
If the pen is damaged, the medicine is cloudy or discoloured, or you can see particles in the solution, do not use it. The UK product information says that Mounjaro should be clear and colourless to slightly yellow.
If the dose counter does not show that the injection has been completed, do not automatically repeat the dose. Follow the Instructions for Use and contact your healthcare professional if you are unsure whether you received the full dose.
Aftercare and Disposal
After each injection, remove the needle and dispose of it according to the disposal instructions you have been given. Do not store the pen with a needle attached.
After the four doses have been given, any excess solution remaining in the pen should be discarded. The UK product information advises that unused medicine and waste should be disposed of in line with local requirements. Your pharmacist can advise you about the correct disposal arrangements in your area.
Following the manufacturer's instructions can help you use each prescribed dose correctly and avoid unnecessary medicine loss. If you are unsure about your injection technique or what to do with your pen, ask your pharmacist or prescriber for help.
Storing Your Mounjaro Pen Correctly
Correct storage is important because unsuitable storage can affect the medicine. These requirements are based on the current UK product information.
| Condition | Requirement |
|---|---|
| Refrigerated storage | 2°C to 8°C |
| Freezing | Do not freeze. A frozen pen must not be used. |
| Unrefrigerated storage | Up to 30°C for a maximum of 30 days after first use, then discard |
| Light | Keep in the original carton to protect from light |
| Handling | Follow the handling instructions supplied with the pen |
| Fridge placement | Store in the refrigerator according to the product instructions |
| After the final dose | Discard the pen according to local disposal requirements |
After first use, Mounjaro KwikPen can be stored unrefrigerated at a temperature not above 30°C for up to 30 days. After this period, the pen must be discarded. Do not freeze the pen.
If you are unsure how to dispose of a used pen or needles, ask your pharmacist about the arrangements in your area.
If Your Pen Genuinely Fails: The Proper Route
If your pen appears to have a problem, there is no need to try to fix it yourself. Taking a few simple steps can help your pharmacy understand what happened.
- Stop using the pen. Do not force it, open it or try to extract the remaining medicine.
- Keep the pen and its packaging, including the batch number and any information shown on the dose window.
- Write down what happened: the date, which dose you were trying to give, what you noticed and how the pen had been stored.
- Contact your dispensing pharmacy. Explain the problem and follow their advice. They can advise whether you need to speak to your prescriber or whether the issue should be reported to the manufacturer.
- Do not change your dose or injection schedule while the issue is being checked. Ask your prescriber what to do if you have missed or only partly received a dose.
- Report suspected medicine or device problems to the MHRA Yellow Card Scheme where appropriate. Patients can report suspected side effects and other safety concerns directly.
If you think your pen has failed, do not try to extract the remaining liquid or use the so called "Mounjaro golden dose". The manufacturer's UK product information says that excess solution remaining in the pen after use should be discarded.
If you are unsure whether you received your full dose, contact your pharmacy or prescriber rather than taking another injection yourself. This can help you avoid accidentally taking more medicine than prescribed.
Mounjaro Strengths, Schedule and UK Pricing
Tirzepatide is a once weekly subcutaneous injection, taken on the same day each week. Doses are increased gradually under prescriber supervision, which is why Mounjaro pens are supplied as four dose, four week units.
According to the authorised UK product information, treatment starts at 2.5 mg once weekly. After four weeks, the dose is increased to 5 mg once weekly. Further increases can be made in 2.5 mg steps after at least four weeks on the current dose, up to a maximum of 15 mg once weekly. Your prescriber will determine the appropriate dose and schedule for you. Not everyone needs to reach the maximum dose.
| Strength | Typical window | Doses per pen | Standard price per pen | Cost per week |
|---|---|---|---|---|
| 2.5 mg | Weeks 1 to 4 | 4 | £174.99 | £43.75 |
| 5 mg | Weeks 5 to 8 | 4 | £204.99 | £51.25 |
| 7.5 mg | Weeks 9 to 12 | 4 | £254.99 | £63.75 |
| 10 mg | Weeks 13 to 16 | 4 | £274.99 | £68.75 |
| 12.5 mg | Weeks 17 to 20 | 4 | £304.99 | £76.25 |
| 15 mg | Week 21 onwards | 4 | £323.99 | £81.00 |
Standard prices as displayed on the product page at the time of writing. The window column shows a typical escalation pattern only and is not a dosing recommendation.
Questions worth asking before buying anywhere
- Is the price per pen, and does one pen provide four doses?
- Is the consultation and prescriber review included, or is there a separate charge?
- Are there delivery charges on top, and how is the medicine handled during delivery?
- Is the medication genuine and supplied through an authorised UK supply chain?
- Is the pharmacy GPhC registered, and are the prescribers appropriately registered in the UK?
- What is the process if a pen arrives damaged or develops a problem during use?
- Is there a charge for the follow up review before your next pen?
Headline prices are not always directly comparable. A lower pen price with a separate consultation fee and delivery charge may result in a higher overall cost. You can compare the full range of weight loss treatment options before deciding.
Who Can Be Prescribed Mounjaro in the UK
Tirzepatide is a prescription only medicine. Whether Mounjaro is suitable for you depends on an individual clinical assessment.
NHS access
NICE technology appraisal TA1026, published 23 December 2024, recommends tirzepatide as an option for managing overweight and obesity in adults who have an initial BMI of at least 35 kg/m² and at least one weight related health condition. NICE advises using a BMI threshold usually reduced by 2.5 kg/m² for people from South Asian, Chinese, other Asian, Middle Eastern, Black African or African Caribbean backgrounds.
NICE also advises that if less than 5 percent of initial weight has been lost after six months on the highest tolerated dose, the prescriber should consider whether continuing treatment is appropriate. NHS England is introducing tirzepatide in phases, so access can vary depending on local services and eligibility.
Mounjaro KwikPen is designed to provide four doses, given as one injection each week. The UK product information also states that some solution may remain in the pen after the four doses have been given. This remaining medicine should not be used as a fifth dose.
If you are wondering how to get the last dose out of a Mounjaro pen, first check whether you have actually received all four labelled doses. If the fourth dose has been given correctly, do not try to extract or inject any remaining liquid. The amount left can vary and is not a measured dose.
If you are concerned about the cost or supply of Mounjaro, speak to your prescriber or dispensing pharmacy about your options rather than trying to use leftover medicine or change your dosing schedule yourself.
Private access
Private providers assess patients against their own clinical criteria, commonly considering a BMI of 30 or above, or 27 or above alongside a weight related health condition. A UK registered independent prescriber reviews your medical history, current medicines, BMI and other relevant information before deciding whether treatment is appropriate.
Speak to a clinician first if
- You are pregnant, trying to conceive or breastfeeding
- You have a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2
- You have a history of pancreatitis or certain digestive conditions
- You take other medicines that may interact with Mounjaro
- You are under 18
Your prescriber can assess your individual circumstances and advise whether Mounjaro is appropriate for you.
For broader context on the routes available, our weight management treatments hub covers the options in more detail.
What the Clinical Evidence Shows
Clinical trials can help explain how tirzepatide performed in a study, but they cannot predict exactly how an individual will respond.
SURMOUNT 1 enrolled 2,539 participants and followed them for 72 weeks. The study reported mean weight reductions of 16.0 percent with 5 mg, 21.4 percent with 10 mg and 22.5 percent with 15 mg, compared with 2.4 percent with placebo. Between 89 and 96 percent of participants receiving tirzepatide achieved at least a 5 percent reduction in body weight, compared with 28 percent receiving placebo.
Gastrointestinal side effects were among the most frequently reported adverse events. Nausea affected approximately 24.6 to 33.3 percent of participants across the tirzepatide groups, compared with 9.5 percent with placebo. Diarrhoea, constipation and vomiting were also commonly reported. Discontinuation because of adverse events ranged from 4.3 to 7.1 percent with tirzepatide, compared with 2.6 percent with placebo.
For UK context, the Health Survey for England 2024 found that 66 percent of adults aged 16 and over were overweight or living with obesity, while 30 percent were living with obesity.
Results vary between individuals. The results seen in clinical trials should not be treated as a guarantee of what you will achieve. Your response can depend on factors such as your health, treatment plan, dose and lifestyle.
Ordering Mounjaro Online in the UK
If you are considering treatment, a regulated online pathway will usually involve several steps.
- Complete a clinical questionnaire covering your medical history, current medicines, height, weight and other relevant information.
- Independent prescriber review. An appropriately registered independent prescriber assesses whether treatment is clinically suitable. Approval is not automatic, and some requests may be declined or referred for further assessment.
- Dispensing from a GPhC registered pharmacy through the appropriate authorised supply chain.
- Suitable delivery and storage handling. Mounjaro needs to be stored within the temperature limits stated in the product information. The pharmacy should use appropriate packaging and handling arrangements for delivery.
- Ongoing review. Your treatment and dose can be reviewed as needed, particularly when your dose is being increased or if you experience side effects.
One practical tip if you are worried about your next pen: start your reorder process before you need your fourth dose. Clinical review and delivery can take time, so planning ahead can help you avoid last minute problems.
You can begin by visiting our Mounjaro injection for weight loss page.
Medical Disclaimer
This article provides general information about Mounjaro and its use. It is not medical advice and does not replace a consultation with a qualified healthcare professional.
Mounjaro (tirzepatide) is a prescription only medicine and should be used under the supervision of an appropriately qualified prescriber. Whether it is suitable for you depends on an individual clinical assessment.
Always follow the Instructions for Use supplied with your pen, together with the advice given by your prescriber and dispensing pharmacy.
Do not use medicine remaining in your pen after the four labelled doses have been given. Do not attempt to divide, transfer or extract solution from the device. Do not change your dose or injection schedule without speaking to your prescriber.
Results and side effects can vary between individuals. Nothing in this article guarantees a particular treatment outcome.
If you experience side effects or have concerns about your treatment, contact your prescriber or pharmacy. NHS 111 can also provide advice when appropriate.
Suspected side effects and problems with medicines or medical devices can be reported through the MHRA Yellow Card Scheme.