How many doses are in one Japanese Mounjaro pen?

One. The pen sold in Japan, マンジャロ皮下注アテオス, is used once and discarded. A month’s supply is four pens. This is different from the KwikPen, which holds four doses.

Is the Japanese pen the same as the pen in the United States?

It is the same kind of device: a single-dose pen with a built-in needle. The box and leaflet are in Japanese, and the written guidance on a missed dose is worded differently. For a pen dispensed in Japan, follow the Japanese instructions and what the doctor tells you.

Do I attach a needle to the Japanese pen?

No. The needle is inside the pen. You do not see it before the injection, and it retracts afterwards. There is no priming and no dial.

How long do I hold the button?

Press the purple button and keep the pen in place until you hear the second click, which takes up to about 10 seconds. If you missed the sound, check that the grey plunger is visible in the clear part of the pen.

Can I split a Japanese pen into smaller doses?

No. It is designed for a single use: the dose cannot be divided or adjusted. If you need a different dose, the doctor prescribes the pen of that strength.

I am part-way through a KwikPen at home. Can I continue with Japanese pens while I am in Japan?

The medicine is the same, but whether to continue and at which dose is for the doctor to decide. At the consultation, tell the doctor your current dose, the date of your last injection and any side effects.

What is Mounjaro called in Japanese?

It is written マンジャロ and pronounced roughly “Manjaro”. The full product name is マンジャロ皮下注アテオス, and tirzepatide is チルゼパチド.

The Japanese Mounjaro Pen (Ateos): How to Use It, and How It Differs from the KwikPen

2026 10/05

English

The Japanese Mounjaro pen: how to use it

Medically reviewed by Dr. Itsuki Nakayama, Director, Almond Clinic Tokyo | Last verified: 5 October 2026

The short version

In Japan, Mounjaro comes as a single-use pen: one pen, one dose. Its Japanese name is マンジャロ皮下注アテオス (Mounjaro Subcutaneous Injection “Ateos”). The needle is built in — nothing to attach, no dose to dial.
If you use a KwikPen at home (the United Kingdom, Australia, Singapore, Hong Kong and others), that is a different device: one pen holds four doses and you attach a new needle each time. Do not use KwikPen steps on the Japanese pen.
The Japanese pen takes three steps: pull off the cap, press flat on the skin and unlock, press the button. You hear two clicks; it takes up to about 10 seconds.
Once a week, on the same day. If you miss a dose, the Japanese guidance turns on whether the next scheduled dose is at least 72 hours away.

The first thing many visitors say after collecting their medicine is: “The box is entirely in Japanese.” The second, from people who use a KwikPen at home, is that the pen looks nothing like theirs. The medicine is the same; the device and some of the written guidance are not. This article walks through the Japanese pen using Japan’s official patient guide.

Please read this first
When you actually inject, go by what the doctor and our staff tell you and by the instructions inside the box. This article is here so that the steps make sense in advance; it does not replace the doctor’s directions. If this is your first time, or you already use tirzepatide at home, say so at the consultation.

Reading the Japanese box

A short glossary for the box and the leaflet — and for searching or asking at a hospital or pharmacy in Japan.

Japanese	Reading	Meaning
マンジャロ	Manjaro	Mounjaro
マンジャロ皮下注アテオス	Manjaro hikachū Ateosu	The product’s full name in Japan; “Ateos” is the name of the pen device
チルゼパチド	Chiruzepachido	Tirzepatide (the active ingredient)
週1回	shū ikkai	Once a week
使用期限	shiyō kigen	Use-by date
2〜8℃で保存	—	Store at 2–8°C
凍結を避ける	Tōketsu o sakeru	Do not freeze

The box shows the dose in the middle of the name, as in マンジャロ皮下注2.5mgアテオス. Check that the dose on the box is the dose you were prescribed before you do anything else.

How the Japanese pen differs from the KwikPen

Both are Eli Lilly’s Mounjaro, both contain tirzepatide, and both come in the same six strengths: 2.5, 5, 7.5, 10, 12.5 and 15 mg. What differs is the device.

	Japan (Ateos)	KwikPen
Doses per pen	1 (0.5 mL), then discard	4 (0.6 mL each), over four weeks
One month’s supply	4 pens	1 pen
Needle	Built in; nothing to attach	A new needle attached for each dose
Priming and dialling	Not needed	Needed each time
After pressing	Two clicks, up to about 10 seconds	Hold and count to 5; check the dose window reads 0
Out of the fridge (below 30°C)	Use within 21 days	Labelling in several countries allows up to 30 days — check your own

The Japanese Mounjaro pen (Ateos, one dose per pen) compared with the KwikPen (four doses per pen)

If you are from the United States, the Japanese pen will look familiar: it is the same kind of single-dose pen. What differs for you is the language on the box and one piece of guidance, on missed doses, covered below.

The two mistakes we see most: assuming one Japanese pen holds four doses (it holds one), and looking for a needle to attach or a dial to turn (there is neither).

The three steps

Before you start, check two things: that the pen is locked, and that the dose and the use-by date are right. Clean the injection site with an alcohol swab.

Pull off the grey base cap. Pull it straight off. Do this just before you inject, and do not put the cap back on.
Place the clear base flat against your skin, then unlock. Keep the base pressed flat against the skin and turn the lock ring all the way to the unlocked position.
Press the purple injection button and wait. The first click means the injection has started; the second click means it is complete. This takes up to about 10 seconds. Do not lift the pen before the second click.

The three steps for the Japanese Mounjaro pen: pull off the grey cap, press flat on the skin and unlock, press the purple button and wait for the second click

If you are not sure you heard the clicks, look at the clear part of the pen: if you can see the grey plunger, the dose has been given. The needle retracts into the pen by itself.

One detail that is easy to miss: do not grip the middle of the pen tightly, or the needle may not retract properly.

Where to inject

Abdomen or thigh — these you can do yourself.
The back of the upper arm only if someone who has been shown how gives the injection for you.
Within the same area, choose a different spot each week rather than the same point every time.
It goes under the skin — not into a muscle and not into a vein.

How it works in Tokyo, and our fees

Once a week: choosing a day, and missed doses

Inject once a week, on the same day of the week. Travel is when this slips most easily, so set a reminder on your phone.

Situation	What the Japanese guidance says
You missed a dose and the next scheduled dose is 72 hours (3 days) or more away	Inject as soon as you remember, then return to your usual day
You missed a dose and the next scheduled dose is less than 72 hours away	Skip the missed dose and inject on your next scheduled day
You want to change your day of the week	Leave at least 72 hours (3 days) since the last injection

Never inject two doses at once.

This is worded differently from the labelling in some other countries, where the instruction is to give a missed dose within 4 days (96 hours) of the missed day. Neither is “wrong”; each country’s approved documents say what they say. Follow the instructions that came with the medicine you are using — for a pen dispensed in Japan, that is the Japanese guidance above.

Crossing time zones: keep to “once a week, same day of the week” by the local date where you are. A shift of some hours does not matter; if you want to move your day, leave at least 72 hours since the last dose.

How the dose is increased

In Japan, treatment starts at 2.5 mg once a week and moves to 5 mg once a week after four weeks. After that, if needed and at the doctor’s judgement, the dose goes up by 2.5 mg at intervals of at least four weeks, to a maximum of 15 mg once a week.

Whether and when to increase is the doctor’s decision, based on how you are responding. It does not happen automatically at four weeks, and pushing the dose up while side effects are still present usually just makes them worse. This is one reason why, if you live abroad, a doctor at home who can follow you over time matters.

Storage, and after use

Refrigerate at 2–8°C, in the outer carton, away from light. Do not freeze, and do not use a pen that has been frozen.
The pen may be kept below 30°C, but in the carton, and used within 21 days. Putting it back in the fridge does not restart those 21 days. More in Travelling with Mounjaro.
Dispose of used pens in line with the rules of the country and local authority where you are. The needle has retracted, but do not put a finger into the base.
If you are taking pens out of Japan, see Taking Mounjaro home from Japan.

Frequently asked questions

How many doses are in one Japanese Mounjaro pen?: One. The pen sold in Japan, マンジャロ皮下注アテオス, is used once and discarded. A month’s supply is four pens. This is different from the KwikPen, which holds four doses.
Is the Japanese pen the same as the pen in the United States?: It is the same kind of device: a single-dose pen with a built-in needle. The box and leaflet are in Japanese, and the written guidance on a missed dose is worded differently. For a pen dispensed in Japan, follow the Japanese instructions and what the doctor tells you.
Do I attach a needle to the Japanese pen?: No. The needle is inside the pen. You do not see it before the injection, and it retracts afterwards. There is no priming and no dial.
How long do I hold the button?: Press the purple button and keep the pen in place until you hear the second click, which takes up to about 10 seconds. If you missed the sound, check that the grey plunger is visible in the clear part of the pen.
Can I split a Japanese pen into smaller doses?: No. It is designed for a single use: the dose cannot be divided or adjusted. If you need a different dose, the doctor prescribes the pen of that strength.
I am part-way through a KwikPen at home. Can I continue with Japanese pens while I am in Japan?: The medicine is the same, but whether to continue and at which dose is for the doctor to decide. At the consultation, tell the doctor your current dose, the date of your last injection and any side effects.
What is Mounjaro called in Japanese?: It is written マンジャロ and pronounced roughly “Manjaro”. The full product name is マンジャロ皮下注アテオス, and tirzepatide is チルゼパチド.

In summary

The Japanese pen is one pen, one dose, three steps: cap off, press flat and unlock, press the button and wait for the second click. There is no needle to attach and no dial, and the dose cannot be split. For a missed dose, go by the 72-hour guidance that comes with the Japanese pen.

This article summarises Japan’s patient medication guide and prescribing information. It is general information, not medical advice; use the medicine as the doctor directs and as the instructions in the box describe. Source: PMDA, 患者向医薬品ガイドマンジャロ皮下注アテオス (updated June 2026). KwikPen details follow Lilly’s instructions for use; check the leaflet supplied in your own country.