If you're using Mounjaro as part of your weight loss journey, you might have heard people talk about a so-called "fifth dose" of the medication. This term refers to the small amount of liquid that can sometimes remain in the Mounjaro injection pen after the fourth dose has been administered. But is this extra liquid safe to use? And why is it there in the first place?
In this blog, the experts at Weight Medics explain what this leftover liquid really is, whether it’s normal, and why it should not be used as an additional dose. We'll also cover safe disposal tips and when to consult your clinician.
Key Takeaways
- The liquid left in the Mounjaro pen is a built-in buffer, not a usable fifth dose.
- This leftover fluid is part of the pen’s design to ensure you receive four full, accurate doses.
- Trying to use this liquid can lead to incorrect dosing—either too much or too little medication.
- The pen should be safely discarded after four doses, even if some liquid remains.
- Speak to your Weight Medics clinician if you're unsure about your dosing schedule or medication disposal.
What Is the “Fifth Dose” in Mounjaro?
After finishing the fourth and final dose from a Mounjaro KwikPen, some users may notice that there's still liquid visible in the cartridge. This leftover medication often gets referred to as the "fifth dose."
However, this is not an actual dose. The pen is engineered to include a small buffer of liquid—essentially a margin of error—to make sure that each of the four scheduled doses is delivered correctly, even if there are minor variations during injection. This leftover is not meant to be used.
Why Is There Liquid Left in the Pen?
The presence of remaining liquid is completely normal and intentional. It’s there to ensure the medication is delivered as accurately and effectively as possible during each weekly dose. This is particularly important for a drug like Mounjaro (tirzepatide), where precise titration and consistent delivery play a major role in both weight loss and diabetes control.
So, while it may look like there's enough for one more injection, that isn’t the case. The pen is only designed to deliver four doses, and the extra fluid isn’t calibrated for safe use.
Can I Use the Leftover Liquid?
In short: No.
Attempting to inject the leftover liquid in hopes of getting a “bonus dose” is not safe. This unmeasured quantity of medication could lead to:
Underdosing, which may reduce the effectiveness of your treatment.
Overdosing, which increases the risk of side effects such as:
- Nausea
- Vomiting
- Diarrhoea
- Constipation
Following the recommended Mounjaro dosage schedule—including slow titration—is vital to helping your body adjust and achieve the best therapeutic outcomes.
What Should I Do With the Remaining Liquid?
Once you’ve taken all four doses from your Mounjaro pen, it should be disposed of in a designated sharps container, even if there’s visible liquid left. Do not try to extract or reuse the remaining fluid.
If you’re unsure about pen disposal or have questions about how to use Mounjaro safely, contact your Weight Medics clinician for advice. Never modify your medication routine without medical guidance.
Final Thoughts: Trust the Process
At Weight Medics, we understand the drive to get the most out of your weight loss treatment—but safety must always come first. While Mounjaro has shown clinically proven results in supporting weight management, it's essential to use the medication exactly as prescribed.
If you're unsure about Mounjaro dosing, titration, or want to explore whether Mounjaro is right for your weight loss journey, our medical team is here to help.
Checked for accuracy by | Jemma Cooke | RGN
What is the “fifth dose” in a Mounjaro pen?
The “fifth dose” isn’t a real dose. It refers to the small amount of liquid that sometimes remains in the Mounjaro pen after you’ve completed the four prescribed injections. This leftover fluid is a built-in buffer designed to ensure you receive four full, accurate doses, not an extra one.
Why is there liquid left after four doses?
The remaining liquid is completely normal and part of the pen’s design. It acts as a margin of safety to make sure each of your four injections delivers the exact amount of medication intended, even if there are small variations during use.
Can the leftover fluid be used as an extra dose?
No, the leftover fluid should never be used. It’s not calibrated for dosing and can lead to inaccurate or unsafe administration. Always discard the pen after completing the fourth dose.
What are the risks of using the remaining medication?
Trying to inject the leftover liquid can cause incorrect dosing, as overdosing can increase side effects such as nausea, vomiting, diarrhoea, or constipation.
How many doses does a Mounjaro pen actually contain?
Each Mounjaro KwikPen is designed to deliver four doses only. Even if you see some fluid left in the cartridge, it’s not an additional usable dose.
What should I do after completing the fourth dose?
After your fourth injection, dispose of the used pen in a designated sharps container, even if some liquid remains. Do not attempt to extract or reuse the leftover medication. If you have any questions about disposal, your Weight Medics clinician can guide you.
Why does the pen design include extra liquid?
The small amount of excess liquid ensures dosing accuracy and reliability. It compensates for any tiny variations in the injection process, so each dose remains consistent and effective throughout your treatment.
How can I ensure accurate dosing with my Mounjaro pen?
Always follow the manufacturer’s instructions carefully and use the pen exactly as prescribed by your clinician. If you’re uncertain about the injection process, your Weight Medics team can demonstrate the correct technique and help you stay on track safely.
