Why is there leftover medicine in my Mounjaro pen?

The Mounjaro KwikPen is designed to give four doses over four weeks and then be thrown away. However, you may have noticed that there's still liquid left in the pen after that fourth dose.

This raises questions. Is this because your pen isn't working properly? Or does it mean you haven't been getting the full dose each time?

Please don't worry. Seeing leftover medication is normal. In fact, the pens are designed this way.

Mounjaro pens are pre-filled with extra liquid. This means that when you follow the instructions, each of your four doses is a guaranteed full dose.

See, the manufacturer has taken into account that you'll lose a little bit of the medication each time you prepare a dose. This happens when you prime the pen and squirt out some of the liquid.

Priming the pen is important because it makes sure there are no air bubbles and the needle is filled with medication. It makes sure you get your full dose every time.

The manufacturer has given you more than enough extra liquid to do the priming squirts. That's why there's always a little bit left after the fourth dose.

Can the leftover liquid be used as a fifth dose?

It's understandable that you wouldn't want to waste medication that could be used. However, the Mounjaro KwikPen is only designed to give four doses. The mechanism won't move beyond that point.

That said, there are posts on social media describing various methods people have used to extract this leftover liquid. These posts sometimes refer to the leftover liquid as the 'magic dose'.

Is it safe to use this so-called 'magic dose'?

Is it safe to use the 'magic dose'?

No. Using the leftover liquid is not standard procedure and Mounjaro's manufacturer warns against it.

The first reason it's not advisable is that you'll likely alter the consistency of your weekly dose.

Each designated dose is 0.6ml. Each KwikPen contains 3ml of medication. Allowing for what you will lose each time you prime the pen, there will usually be less than 0.6ml left.

It's not good to give your body a smaller dose for a week. You can expect poorer results that week – and if your next pen has a stronger dose, it will be more difficult to adjust. This could mean more severe Mounjaro side effects, such as nausea, vomiting or diarrhoea.

The second reason relates to extracting the leftover liquid. To achieve this, you'd either have to break the mechanism of the pen or use a separate syringe to draw the liquid out. This could compromise the medication and leave you vulnerable to infection.

The manufacturer, Eli Lilly, gives very clear instructions regarding this leftover medication:

"After four doses covering a month's treatment, throw away (discard) the KwikPen, including the unused medication. The KwikPen will prevent you from dialling a full dose after you have given yourself four weekly doses.

"Do not transfer solution from your MOUNJARO KwikPen into a syringe. Do not inject the leftover medication."

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