How to Apply a Mounjaro KwikPen (Plain-English UK Guide, October 2026)

01 · The core answer

How to apply the Mounjaro KwikPen each week

Mounjaro is injected under the skin (subcutaneously) once a week, on the same day each week, at any time of day, with or without food.¹ Everything else is about doing that cleanly and consistently. Your pen comes with a patient information leaflet, and its illustrated steps are the final word on fitting the needle, priming and delivering the dose.¹³

Small details such as how to prime, how long to hold the pen in place and when to remove the needle matter, so follow the leaflet. If you want a companion walk-through, our injection step-by-step guide covers the same ground from the injection side.

If you are still deciding whether treatment is right for you, start with the process of applying for Mounjaro or look at our KwikPen prescription explainer. Mounjaro is a prescription-only medicine, supplied after an online consultation reviewed by a GPhC-registered prescriber.¹

You can see doses and current prices on the Mounjaro pen page, where all six strengths are in stock. Needles, a sharps bin and injection guidance are included with every order, so you are not left to source them yourself.

02 · Choosing your injection site

Choosing your injection site

Three areas are licensed for Mounjaro, and the stomach is the one most people use. 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.¹

The upper arm is hard to reach and see yourself, which is why it needs a helper. If you live alone, the stomach and thigh are the practical choices. Rotate the site with each dose.¹ Rotating does not need to be elaborate: many people simply alternate sides of the stomach, then move to a thigh, then return. Keeping a note in your phone or in the free GLPTrackr companion app makes it easy to remember where you went last.

Choose skin that is intact and comfortable. If a spot is sore, bruised or irritated, pick another area and mention persistent skin reactions to your prescriber. Any new or worrying symptom can also be reported through the Yellow Card scheme.¹⁹

03 · Dial, window and clicks

Dial, window and clicks: what to trust

The window is the only thing you should trust when setting a dose.

Do not count clicks. People often ask how many clicks are in a Mounjaro pen, but clicks are a feel-and-sound cue, not a measurement. If you are unsure, look at the window again before injecting.

Why the pen will not turn any further

The pen will not turn to a full dose once the four doses are used.

Do not try to top up from another pen or combine leftovers. Contact the pharmacy that supplied it, or our support team if you ordered from us. For the physical size and layout of the pen, see our page on Mounjaro pen dimensions.

04 · Missed doses and day changes

Missed doses and changing your injection day

Most mistakes with timing are easy to fix if you follow the licensed rule. 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

You can also move your weekly day if your routine changes. You can change your weekly injection day if needed, as long as at least 3 days (72 hours) have passed since your last dose.¹

Picking a day you will keep

There is no "best" time of day — Mounjaro works the same morning or evening, with or without food. What matters is the same day each week.¹ Many people choose a weekend morning so early side effects fall on days off, but that is a convenience, not a rule. Link the injection to something you already do weekly, set a phone reminder, and treat it like any other fixed appointment.

05 · Storage and travel

Storing your pen and travelling with it

Unused pens live in the fridge; the pen in use has a little more flexibility. 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 — useful for short trips — and must then be thrown away. Do not use a pen that has been above 30°C. Keep the pen cap on to protect it from light, and never use a pen that has been frozen.¹

Unopened pens should be kept in the fridge and keep until the expiry date printed on the box. 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, because figures circulating online often come from other countries' labels.¹

Flying and holidays

You can fly with Mounjaro. Carry pens in hand luggage (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. Check destination rules for travelling with prescription injectables before you fly.¹

06 · Mistakes to avoid

Common mistakes and what to do instead

Most problems come from improvising. The pen is designed to deliver a fixed licensed dose, and anything that bends that design adds risk without a benefit.

• Doubling up after a gap. Never take two doses within 3 days of each other.¹
• Leaving a pen out of the fridge unnoticed. Check the in-use limit and discard once it passes.¹
• Using a frozen pen. Never use one that has been frozen.¹

07 · After the injection

After the injection: what is normal

You will not feel a dramatic change on injection day, and that is expected. The starting weeks are about adjustment rather than weight loss itself. Everyone starts Mounjaro on 2.5mg once a week, and 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 up to a maximum of 15mg weekly, depending on how you respond and tolerate it.¹

Some people notice appetite change and early loss in week one, others feel little until a higher dose — both are normal. Mild nausea, altered appetite and tiredness in the first days after each injection are the commonest early effects and usually settle.¹ If symptoms are severe or do not settle, speak to your clinical team rather than pushing through or changing the dose yourself. 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.

How did I know it went in correctly?

There is no test you can do afterwards. If you followed the leaflet, set the dose by the window and injected under the skin at a licensed site, the dose has been delivered. If anything felt wrong, such as the pen not completing as the leaflet describes, do not repeat the dose to compensate. Contact our support team or your prescriber, who can advise on what to do before your next scheduled injection.

08 · What treatment is for

What the injection is for

Mounjaro is the brand name for tirzepatide, a once-weekly injectable prescription medicine made by Eli Lilly. In the UK it is licensed for weight management in adults and for type 2 diabetes.¹ It works alongside a reduced-calorie diet and increased physical activity, not instead of them. For more background, see our Mounjaro description.

In the SURMOUNT-1 trial of 2,539 adults, people taking tirzepatide alongside diet and exercise lost on average 15% of their body weight on 5mg, 19.5% on 10mg and 20.9% on 15mg over 72 weeks, compared with 3.1% with lifestyle changes alone. These are trial averages — individual results vary.²

Weight loss on Mounjaro is gradual by design. Think in months, not days, and judge progress by trend, not individual weigh-ins.¹ Applying the pen correctly and on schedule is the part you control. Our weight loss clinic page explains the wider support around treatment, and if you are exploring the public route, see how to apply for Mounjaro on the NHS.