If you are looking for a Mounjaro manual, this is a practical guide to using the Mounjaro KwikPen correctly: it is a single-use, pre-primed injection pen, so you do not prime it or attach a needle for repeated use, and each weekly dose should be given with a new pen exactly as set out in the Instructions for Use in your pack.
The first injection is the part most UK adults prescribed Mounjaro for weight management feel least certain about, and the device is simpler than expected once you have seen how it works.
This guide covers how the Mounjaro pen works, the injection sequence, site rotation, dose timing, storage, disposal, what to do about your second dose and beyond, and the questions that come up most, including the priming question that causes more confusion than anything else. Using the KwikPen properly matters for both treatment effect and safety, especially when you are trying to avoid mistakes around dose scheduling, pen handling, or missed doses.
It is a companion to the Instructions for Use supplied in your pack, not a substitute for it. Read that leaflet before your first injection, and follow the guidance your prescriber or pharmacist gave you. Details of Mounjaro treatment, including the strengths supplied, are on our product page.
How the Pen Works
Mounjaro in the UK is supplied in a single-dose pre-filled pen, commonly called the KwikPen.
Three things about the device explain most of the questions people arrive with:
It is single-use. One pen delivers one weekly dose, then it is finished and goes in your sharps bin. You do not save it, refill it, or take a second dose from it.
It is pre-primed. The manufacturer has already prepared it. There is nothing for you to do before injecting.
The needle is already attached and hidden. You do not fit a needle, and you should not see one. The pen covers it before, during and after the injection.
This is a different design from some other weight-loss and diabetes pens, which is where the confusion usually starts.
Do You Need to Prime the Mounjaro Pen?
No. The Mounjaro KwikPen does not require priming, before your first dose or any dose after.
There is no priming step, no air-shot, and no test dose. If you have been told otherwise, that guidance was for a different device.
The reason this question comes up so often is that multi-dose pens do need priming. Semaglutide pens such as Wegovy and Ozempic, and most insulin pens, hold several doses and require a flow check before the first use of each pen. People moving between treatments, or reading general injection-pen advice, reasonably assume the same applies here. It does not.
If your pen appears not to have worked, do not attempt to prime it or inject again. Contact your pharmacist or prescriber. Taking an unplanned second dose is a bigger risk than missing one.
Before You Inject
Check the pen. Confirm the name and strength on the label match what you were prescribed, and check the expiry date. Look at the medicine through the window; it should be clear and colourless to slightly yellow. Do not use it if it is cloudy, discoloured, or has particles in it.
Let it come closer to room temperature if it is cold. The Instructions for Use explains how long to allow. Injecting straight from the fridge can be more uncomfortable, though it is not unsafe.
Do not use a pen that has been frozen, or one you believe has been left out of refrigeration beyond the permitted period. Ask your pharmacist rather than guessing.
Wash your hands and have your sharps bin within reach before you start.
Where to Inject and How to Rotate Injection Sites
This is where to choose the mounjaro injection site: the abdomen, the thigh, and the upper arm, as an subcutaneous injection given at a 90° angle. The upper arm generally needs someone else to do it.
Avoid the area immediately around the navel or belly button, and any skin that is bruised, tender, injection site red, hard, scarred or broken.Mild redness or irritation usually settles on its own. Seek medical advice if the reaction is severe, persistent or getting worse.
Rotate sites each week. Repeated injection into the same spot can cause the tissue to change, which affects both comfort and absorption. Some people work around a rough rotation to keep track, and switching to another area can also reduce discomfort because the skin may respond differently from one spot to another. It does not need to be elaborate, only different each time.
The Injection
The exact sequence is set out in the Instructions for Use in your pack, and you should follow that document rather than any summary. In general terms:
- Clean the site and let it dry.
- Remove the base cap just before injecting. Do not put it back on.
- Place the pen flat against the skin, following the orientation shown in your Instructions for Use.
- Press and hold the dose button as directed in the leaflet.
- Keep the pen against the skin after pressing the button and hold it in place as you slowly count to 5. This is where people go wrong most often, lifting away early before the injection has fully finished.
- Check the indicator described in your Instructions for Use to confirm the correct dose was delivered.
- Dispose of the pen in your sharps bin immediately, without recapping.
A small amount of bleeding or a bead of liquid at the site happens sometimes and does not usually mean the dose was lost. If needed, lightly press with gauze or cotton, but do not rub the area. The injection usually causes only mild discomfort and should not cause severe pain. If the injection hurt more than you expected, review your technique and speak to your pharmacist or prescriber rather than repeating the dose.
Your First Injection
Ask to be shown. Your pharmacist or prescriber can demonstrate. Many people find one demonstration helps them feel more confident. Unlike devices that require a new needle to be fitted before each injection, this pen is designed for single use. This is a routine request and worth making.
Beyond that, three things help:
Pick your day. You will be injecting weekly on the same day, so choose one that suits your routine. A reminder helps in the early weeks.
Do not rush the hold. The most common first-time error is lifting the pen away before the dose has fully delivered.
Expect the noise. The pen makes a distinct sound when it fires and often a second sound as it finishes. That is normal.
Your Second Dose and Beyond
The most common second-dose question is whether you reuse the first pen. You do not. Each dose comes from a new pen, every week, for the life of your treatment.
Otherwise the process is identical each time. Same day of week, new pen, different site. Before moving to your next dose, check that you received the full mounjaro dose.
Two situations worth knowing:
If you miss a dose, if it has been 4 days or less, take the missed dose; if it has been more than 4 days, skip the missed dose. Do not take two doses together. You can change your injection day by taking it a day early, as long as there are at least 3 days between two Mounjaro doses.
When your dose is increased, Mounjaro follows a gradual titration schedule to minimise side effects, and the maximum adult dose is 15 mg once weekly. The pen will be a different strength but works the same way. Confirm the strength on the label matches your new prescription before injecting. Dose changes are made by your prescriber following review, never adjusted by taking more from a pen.
Storage and Disposal: Using a Sharps Bin
Store pens refrigerated at 2°C to 8°C. Do not freeze them, and do not use one that has frozen. A pen may be kept below 30°C outside the fridge for up to 21 days, and once that allowance is used it cannot be reset by refrigerating again.
Keep pens in the original carton, away from light, and out of the sight and reach of children.
Used pens go straight into a sharps bin or approved sharps container for proper disposal, never into household waste or recycling. Your pharmacy can advise on obtaining a bin and on local arrangements for returning full ones, which differ between council areas.
When to Ask for Help
Contact your pharmacist or prescriber if you are unsure whether a dose was delivered, if a pen appears damaged or faulty, if the medicine looks wrong, if you have a reaction at the injection site that does not settle, if you develop signs of an allergic reaction or other hypersensitivity reactions.
Symptoms of dehydration should also be monitored, especially if gastrointestinal side effects are significant.
Tell your prescriber if you have a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2, as Mounjaro may not be suitable.
Mounjaro may reduce the effectiveness of oral contraceptive pills, particularly after starting treatment and after dose increases. Follow your prescriber's advice and the patient information leaflet.
Suspected side effects and suspected device faults can both be reported through the MHRA Yellow Card scheme.
Getting the injection right is only part of treatment. Mounjaro is prescribed alongside dietary and physical activity support, and if you want to understand how it sits within the wider range of medically supervised weight loss options, your prescriber can talk that through at review.
