Mounjaro Pen Change: When and How to Swap Your Pen and Needle (October 2026)

01 · The short answer

When do you change your Mounjaro pen?

You change your Mounjaro pen once you have used its four weekly doses. Mounjaro is injected under the skin once a week, and each KwikPen contains four weekly doses.¹ After the fourth injection, that pen is finished and your next weekly dose comes from a new pen. The new pen may be the same strength or a higher one, depending on what your prescriber has agreed with you.

You do not need to judge this by eye: when the pen has delivered its four doses, it will not turn to a full dose. That is your signal to put it aside for disposal and start the next pen.

If your pen looks different from the one in your last box, or the plunger or window seems unfamiliar, read the leaflet in your box and contact us. The dose in the window and the strength printed on the pen are what matter, and both are the same for the same strength of Mounjaro.

02 · What to decide

Pen change, needle change or dose change?

• Changing the pen: you do this after four weekly doses. You are simply moving on to the next pen in your supply.
• Changing the needle: this is about the needle fitted to the pen, not the pen itself. Follow the patient information leaflet for how to attach and remove it. Pen needles and injection guidance are included with every order, and our complete guide to the needle for a Mounjaro pen covers the practical side.
• Changing the dose: this is a clinical decision. Pens come in fixed strengths of 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg and 15mg, and your prescriber decides when to move up, hold or step down. Our page on whether you can change the dose on a pen explains why you cannot adjust it yourself.

If you are not sure which of these applies to you, check the strength printed on your current pen, the strength on your next pen and what your prescriber last told you. If those do not match, ask before injecting.

03 · Next step

What to do next

If your pen is finished, check that your next pen is ready and stored correctly. If you are running low and need a repeat, our Mounjaro pen prices and consultation page shows the current price of every strength: the 2.5mg pen is £169.99 per month at standard price, and all six doses are in stock. Repeat orders re-check suitability, and there is no auto-shipping, so order before you run out.

For the wider picture on treatment, our weight loss clinic explains how reviews, titration and aftercare work. Your prescribing team stays involved throughout, including monthly reviews and side-effect support.

Use each pen exactly as it was designed. Do not look for a way to get more out of a pen, and do not change the dose yourself. The pen is built to deliver four weekly doses accurately, and anything beyond that means unknown dosing accuracy and no safety data.¹

04 · How many doses per pen

How many doses does a Mounjaro pen hold?

A Mounjaro KwikPen holds four weekly doses, whatever its strength. Mounjaro (tirzepatide) is a once-weekly injectable prescription medicine made by Eli Lilly, supplied as a pre-filled multi-dose pen in six strengths: 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg and 15mg.¹ Each KwikPen contains four weekly doses.¹ So one pen covers roughly a month of treatment, and a new pen starts after your fourth injection.

People often ask whether all Mounjaro pens have four doses. The answer from the product information is yes: the pen is a multi-dose pen built around four weekly doses. What changes between strengths is how much tirzepatide each dose contains, not how many doses the pen holds.

How the pen tells you what is left

The KwikPen is set by turning the dose knob until the dose indicator shows the correct dose in the window. Click counting is not the way to confirm anything. The window is.

In practice, this means that when you reach the end of the fourth dose, the pen has done its job. You do not need to guess whether anything remains, because the pen will stop you.

Keeping track of your four doses

Because you inject on the same day each week, it is easy to lose count, particularly if you take a break or travel. A few simple habits help:

• Note the date of each injection somewhere you will see it, such as a phone reminder or a calendar.
• Our free companion app, GLPTrackr (iOS and Android), is designed for tracking a GLP-1 journey, including your injections.

If you are ever unsure whether you have injected this week, do not inject again to be safe. Check your notes, and if there is still doubt, contact the prescribing team before your next dose.

For a fuller walk-through of getting a new pen ready, see our guide to preparing a Mounjaro pen, and always keep the patient information leaflet from the box to hand.

05 · Changing the needle

How to change the needle on a Mounjaro pen

To change the needle on your Mounjaro pen, follow the step-by-step instructions in the patient information leaflet that comes with your pen. The leaflet is the instruction for attaching and removing the needle on your specific pen version.¹³

What you need to have to hand

Pen needles are separate from the pen itself. Needles, a sharps bin and injection guidance are included with every EverydayMeds order, so you should not find yourself with a pen and nothing to fit to it. If you need more, you can buy pen needles separately. Before injection day, check that you have a needle, your pen, somewhere clean to work and your sharps bin within reach.

Why people ask about changing the needle

Some people are on their first pen and unsure how the needle goes on. Some have started a new pen and want to know whether the needle comes with it. Others have had a needle that seems blocked, bent or uncomfortable and want to know whether to swap it. In each case the right first move is the same: read the leaflet and, if anything seems wrong with the needle, do not push on regardless.

Our companion guides go further on the practical points: the complete UK guide to needles for the Mounjaro pen and the guide to needle safety and side effects.

Things to avoid

• Do not use a damaged pen or a needle that looks bent or blocked. Set it aside and contact us.
• Do not share pens or needles with anyone else. Our page on sharing a Mounjaro pen explains why.
• Do not guess at the instructions from memory or from a video made for a different pen. Pens differ between medicines and versions, and the leaflet for your own pen is the one that applies.
• Do not put used needles in household bins. Use your sharps bin and follow local disposal arrangements.

Licensed injection sites are the stomach area (at least 5cm from the belly button), the front of the thigh, or the back of the upper arm if someone else gives the injection. Rotate the site with each dose.¹ If you find injections uncomfortable, mention it at your monthly review. Support with technique and side effects is part of the aftercare we provide, and a small adjustment is often all that is needed.

06 · Leftover medicine and extra doses

Why is there still some Mounjaro left in my pen?

Some liquid can remain in a pen after your fourth weekly dose, and that is not a spare dose. A pen contains four weekly doses and is designed to deliver four.

You may see online discussion of getting more out of a pen, sometimes with nicknames. We do not support that: the pen is designed to deliver four doses. Altering doses outside the licence means unknown dosing accuracy and no safety data.¹

Why a partial dose is a problem

If a pen cannot dial a full dose, any attempt to combine what is left with a second pen means you cannot be sure what you have actually received. The same applies to trying to split a dose across days or injecting more often than weekly.

What to do instead

• Treat the finished pen as finished and start your next pen on your usual injection day.
• Dispose of the used pen safely, as set out in the leaflet and your local arrangements.
• If a dose seems to have gone wrong, for example the pen leaked or you are unsure whether you received a full dose, do not repeat it on your own. Contact the prescribing team before taking any further dose.

If you want a lower or gentler dose

If the idea behind a smaller dose is that side effects are too strong, there is a proper route. Tell your prescriber at your monthly review or sooner by contacting support. That keeps your dosing accurate and your treatment safe.

If you suspect a side effect, you can also report it through the MHRA Yellow Card scheme.¹⁹ If the pen itself seems faulty, our page on a broken Mounjaro pen explains what to do.

07 · Moving to a new strength

Changing to a different strength of pen

You move to a different strength only when your prescriber says so, and the new strength arrives as a new pen. Everyone starts Mounjaro on 2.5mg once a week. This starting dose is about letting your body adjust, not about weight loss itself. After at least 4 weeks the dose increases to 5mg, and can then step up by 2.5mg at a minimum of 4-week intervals (7.5mg, 10mg, 12.5mg) up to a maximum of 15mg weekly, depending on how you respond and tolerate it.¹¹¹

Many people settle at a maintenance dose of 5mg, 10mg or 15mg. Higher is not automatically better, and your prescriber will guide the right pace.¹

You cannot turn one pen into another strength

A common question is how many clicks to use for 5mg from a 7.5mg pen. The answer is that you do not do that. Each pen is a fixed strength, the window confirms the dose that pen delivers, and clicks are not a measure you can rely on. Using a higher-strength pen to deliver a lower dose is dose-altering outside the licence. If you have the wrong strength, contact the prescribing team rather than improvising. Our page on changing the dose on a Mounjaro pen goes into this in detail.

Switching to us from another provider

If you are changing provider and arriving on a higher dose, you do not have to restart on 2.5mg for the sake of price. A new customer gets £40 off their first order at any dose with code FIRST40, and every later order is £25 off the standard price (code DOSE25). Standard prices are £169.99 for 2.5mg, £189.99 for 5mg, £244.99 for 7.5mg, £274.99 for 10mg, £289.99 for 12.5mg and £299.99 for 15mg, each per month. Whether a higher starting strength is appropriate is a decision for our prescriber after your consultation, based on your history.

Measuring your own progress

Moving up a strength is not a race. The first weeks on 2.5mg are an adjustment phase, and most measurable progress builds from 5mg onward, month by month.¹ If you have questions about measurements and what counts as progress, our Mounjaro measurements page can help.

08 · Storing pens during a change

Storing your old and new pen

Keep your next pen in the fridge and your in-use pen according to the in-use rule. Keep Mounjaro pens in a fridge at 2–8°C and never freeze them. Once in use, a pen can be kept out of the fridge at a temperature not above 30°C for up to 30 days after first use, and must then be thrown away. Keep the pen cap on to protect it from light, and do not use a pen that has been above 30°C or has been frozen.¹

This matters at the point of changing pens because you are now handling more than one pen at once. A sensible routine is to leave unopened pens in the fridge until you need them, and take the next one out only when you are ready to start it. Unopened pens keep until the expiry date printed on the box.¹³

The 30-day in-use rule

The 30 days (not above 30°C) applies to a pen once you have started using it. Because a pen holds four weekly doses, you will normally finish it well inside that window if you inject every week. If you have paused treatment or delayed a dose, check the date you opened the pen. If it has passed 30 days, discard it even if some liquid appears to remain. Writing the opening date on the box makes this easy to check.

If an unopened pen has been out of the fridge

If an unopened pen has been out of the fridge, check with the pharmacy before using it rather than relying on a remembered day limit. Figures circulating online often come from other countries' labels, and the UK pen's labelling is what applies to you.¹ Contact us and we will advise.

Travelling when it is time to swap

You can fly with Mounjaro. Carry pens in hand luggage, because hold luggage can fall below freezing, ideally in a cool bag with the prescription label or a copy of your prescription. In-use pens tolerate up to 30 days not above 30°C, so most holidays need no special arrangements. For hot climates use an insulated pouch, and check destination rules for travelling with prescription injectables before you fly.¹ If your trip will cross a pen change, take the next pen with you in the same hand luggage rather than relying on finding a fridge at the other end.

Disposal of the finished pen

When a pen is finished, do not leave it lying around, and do not put it in household waste. Use your sharps bin, which is included with every order, and follow your local arrangements for disposal.

09 · Timing and missed doses

Timing your first injection from a new pen

Your first injection from a new pen follows the same weekly schedule as before: the same day each week. Mounjaro is injected once a week on the same day each week, at any time of day, with or without food.¹ There is no best time of day: Mounjaro works the same morning or evening. What matters is the same day each week, so pick a day and time you will remember. Many people choose a weekend morning so early side effects fall on days off.

If you are late starting the new pen

If you miss a dose, take it as soon as you can within 4 days (96 hours) of the scheduled time, then carry on with your usual day. If more than 4 days have passed, skip the missed dose entirely and take the next one on your normal day — never take two doses within 3 days of each other.¹ This is the rule to use if your next pen did not arrive in time or you forgot to start it.

Is it safe to inject every 5 days?

No. Mounjaro is a once-weekly medicine, and you should never take two doses within 3 days of each other. Injecting more often than the schedule allows is not something to do on your own initiative. If you want to change the weekday you inject, that is permitted within a limit: you can change your weekly injection day if needed, as long as there are at least 3 days between two doses.¹ That is the safe way to move your day, rather than injecting early to fit a pen change into your week.

Why the weekly rhythm matters

Tirzepatide has a half-life of about five days, so after a final dose it takes roughly four to five weeks to clear the system.¹ That long tail is why a short delay does not undo your progress, and also why doses should not be bunched together. The medicine builds up and clears over days, not hours.

Early weeks after starting or restarting

Mild nausea, altered appetite and tiredness in the first days after each injection are the commonest early effects and usually settle. If you have restarted after a long gap, speak to your prescriber before choosing which strength to take, rather than assuming you can pick up where you left off. Our monthly reviews exist for exactly this kind of question, and repeat orders re-check suitability each time.

If you would like to understand how the pen is prepared before the first dose from a new pen, read our guide to preparing your Mounjaro pen.

10 · Pen problems and what to do

What if the pen will not work properly?

If your pen will not dial, will not inject or looks damaged, stop and do not force it. That is often mistaken for a fault when it is actually the end of the pen.

Telling a finished pen from a faulty one

A pen that has delivered its four weekly doses will stop turning to a full dose. That is normal. A faulty pen behaves differently: it may be cracked, leaking, stiff from the outset, or unable to dial even though you have not yet used four doses. Count your injections from your notes first. If you have used four, start the next pen. If you have not, and the pen will not work, treat it as a possible fault.

What to do with a faulty pen

• Keep it, with the box, and contact our support team (Monday to Friday, 9am to 5pm) by email at support@everydaymeds.co.uk, through your account portal chat or by phone on 0333 207 0413.
• Dispensed prescription medicines cannot be returned except for a faulty, damaged or wrong item, and you should contact us within 3 days.
• Do not inject a replacement dose until you have spoken to us. While the issue is sorted, if you miss a dose, take it within 4 days (96 hours) of the scheduled time, otherwise skip it — never take two doses within 3 days of each other.

For detailed troubleshooting, see our pages on how to unjam a Mounjaro pen and what to do with a broken Mounjaro pen. If you want to understand the physical size of the pen for carrying it, our page on Mounjaro pen dimensions covers it.

Reporting problems

If you think a pen problem caused you a side effect or a wrong dose, you can report it through the MHRA Yellow Card scheme.¹⁹ Reporting helps the regulator spot patterns, and it does not replace speaking to your prescriber.

Vial or pen?

People sometimes ask about the difference between a Mounjaro pen and a vial, and why air is pushed into a vial. Mounjaro in the UK is described in the product information as a pre-filled multi-dose pen, the KwikPen, and that is the product we supply.¹ We do not supply vials and cannot advise on drawing up a medicine from one. If someone offers you Mounjaro in a vial, or offers to supply without a consultation or prescription, treat it with caution. Buy from a registered UK pharmacy, and you can check ours on the GPhC register under registration 9012878.

11 · Getting your next pen

Getting your next pen on time

The simplest way to avoid a gap at your pen change is to reorder before your fourth dose. Because each pen holds four weekly doses, you know to the week when it will run out, so plan your reorder with room for review and delivery rather than waiting until the fourth injection.

How a repeat order works with us

Repeat orders re-check suitability, and there is no auto-shipping, so you stay in control. Your order is reviewed by a GPhC-registered prescriber, and if the prescriber decides the treatment is not suitable, the order is refunded automatically in full. Once dispensed by our registered pharmacy, same-day dispatch applies when ordered by 3pm. Delivery is free next-day tracked delivery in temperature-controlled, discreet packaging, and Saturday delivery is £14.99. The consultation is free, and the price shown is the price paid.

Every future order after your first is £25 off the standard price with code DOSE25, and a new customer's first order is £40 off with code FIRST40. Current prices were checked 25 October 2026, and stock is shown as in stock on the Mounjaro pen page. Payment options include Visa, Mastercard, Klarna and pay-monthly plans, with no subscription lock-in.

Why we supply as we do

Our Mounjaro comes via official LillyDirect supply, direct from Eli Lilly's UK distribution, as genuine KwikPens. All six doses are stocked, from 2.5mg to 15mg. More than 100,000 customers have been supported by EverydayMeds, which is a measure of how many people we have served, not a promise about results.

NHS or private?

Mounjaro is available on the NHS, but access is being phased in over several years. NICE recommends it for adults with a BMI of at least 35 plus at least one weight-related condition, and the NHS primary-care rollout began in June 2025 with the highest-need groups first (initially BMI 40+ with four or more qualifying conditions).⁴⁶ Full rollout is expected to take years, which is why many people who meet the licensed criteria choose regulated private treatment rather than waiting. Whichever route you take, the pen and the four-dose rhythm are the same.

Mounjaro (tirzepatide) is a prescription-only medicine, supplied only after an online consultation reviewed by a GPhC-registered prescriber. It is used alongside a reduced-calorie diet and increased physical activity. Individual results vary. This page is information, not a substitute for medical advice.

12 · Serious side effects

Serious side effects: when to get help straight away

Serious side effects are uncommon but need urgent attention. Seek immediate medical help for: severe, persistent stomach pain that may spread to your back, with or without vomiting (possible pancreatitis); pain in the upper right abdomen, fever or yellowing of skin/eyes (possible gallbladder problems); or signs of a severe allergic reaction such as swelling of the face or throat and difficulty breathing. If you take insulin or a sulfonylurea alongside Mounjaro, watch for low blood sugar (shakiness, sweating, confusion) — your prescriber may need to adjust those medicines.¹