When to Prime a Mounjaro Pen — and When to Skip It
Priming is the process of preparing a new pen by releasing a small amount of medicine into the air to remove air bubbles and confirm the pen is working. For Mounjaro, this is done once only, on the very first use of a brand-new pen. Once the pen has been primed, you do not prime it again for any subsequent injections from the same device.
Why priming matters the first time
A new pen may contain a small air bubble at the tip of the needle or within the cartridge. Priming clears this before your first injection, so you can be confident you are receiving the full dose. Skipping the first-time prime on a new pen could mean an incomplete dose.
What about Wegovy — is it the same?
Wegovy (semaglutide) pens have their own preparation steps, which differ from Mounjaro. If you are using Wegovy or switching between the two, always refer to your individual pen's patient information leaflet for the correct steps. You can also read about how to prime a Wegovy pen for a side-by-side understanding of the differences.
A note on instructions
The exact priming steps — how many clicks, what to look for — are described in the patient information leaflet that comes with your pen and on the electronic Medicines Compendium (eMC) product information for Mounjaro. These are the authoritative sources for your specific pen and should always be your first reference. For a full walkthrough, see the guide on how to prime a Mounjaro pen step by step.
If you are ever uncertain whether your pen has been primed or used before — for example, if the pen has been handled by someone else or the label is unclear — check with your prescriber or pharmacist before injecting. It is also worth knowing that how long you stay on Mounjaro is a separate decision made with your prescriber, unrelated to pen handling.
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Keeping Track of Your Doses with GLP Trackr
One of the easiest ways to avoid confusion about whether a pen is new or already in use is to log each injection as you give it. GLP Trackr's dose logging feature lets you record the date, time, and dose strength of every injection, so you always have a clear, timestamped record of exactly where you are in your treatment.
Because Mounjaro is a once-weekly injection, it can sometimes be hard to remember whether this week's pen is fresh out of the box or was started last week. With a dose log in the app, that guesswork disappears — you can see at a glance when your last injection was and which dose you used.
GLP Trackr also sends gentle dose reminders, so your weekly schedule stays on track without relying on memory alone. Together, logging and reminders mean you spend less mental energy on the logistics and more on the journey itself.
Always follow the specific pen instructions in your patient information leaflet, and if anything about your pen's preparation feels unclear, contact your prescriber or pharmacist — they know your full history and can advise you directly. GLP Trackr is a tracking tool, not a substitute for that guidance.
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For a broader overview of managing your Mounjaro journey, visit the Mounjaro hub.
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Frequently asked questions.
No. You only prime a Mounjaro pen once — the first time you use a brand-new pen. For all subsequent injections from that same pen, no priming is needed. Always check the patient information leaflet that came with your pen for the exact steps.
Skipping the first-time prime on a new pen may mean an air bubble is present, which could affect the dose delivered. If you are unsure whether your new pen was primed correctly, speak with your prescriber or pharmacist before your next injection.
Wegovy pens have their own preparation instructions, which differ from Mounjaro. Check the patient information leaflet for your specific Wegovy pen to confirm whether and when priming is required, as steps vary between devices and manufacturers.
Check the dose counter or window on the pen — used pens will show a changed indicator depending on the device. If you are genuinely unsure whether a pen is new or already in use, contact your prescriber or pharmacist rather than guessing.
GLP Trackr lets you log the date, time, and dose of every injection, giving you a clear record of when each pen was started. Dose reminders also help you stay on your weekly schedule without relying on memory alone.