Overview
Whether you are using Mounjaro® or Wegovy®, you may notice a small amount of liquid remaining in the pen after you have completed your four scheduled weekly doses. This is a normal part of the pen's design and does not mean your treatment was unsuccessful or incomplete.
This article explains:
Why residual liquid remains in the pen.
Whether the remaining liquid should be injected.
The different disposal timelines for Wegovy and Mounjaro.
Important storage reminders following the May 2026 delivery update.
Why residual liquid remains in the pen
Both Mounjaro® and Wegovy® pens are manufactured with a small additional volume of medication beyond the four required doses. This extra liquid is intentionally included by the manufacturer to ensure:
Accuracy: The full weekly dose is delivered correctly every time.
Priming: The small amount of liquid used to prime the pen (clearing air bubbles) does not reduce your actual treatment dose.
Consistency: Dosing remains reliable from the first week to the fourth.
Because of this specific design, it is physically impossible to empty the pen completely during normal use.
Should the remaining liquid be used?
No. The residual liquid left in a finished pen is not a measured dose and must not be injected. Attempting to extract or inject the remaining liquid could result in an inaccurate dose, which may lead to increased side effects or reduced effectiveness of your treatment. Once you have completed your four scheduled weekly doses, the pen is considered finished, even if liquid is still visible through the window.
When to dispose of your pen
While both pens contain four doses, their "in-use" life differs. You must dispose of your pen when the first of the following conditions is met:
Mounjaro® Disposal
All four weekly doses have been used, OR
30 days have passed since the first use.
Wegovy® Disposal (UK Guidance)
All four weekly doses have been used, OR
6 weeks (42 days) have passed since the first use.
Safe disposal should always follow sharps container guidance for injectable medications.
Storage and Delivery (May 2026 Update)
Following updated UK clinical standards as of May 2026, please note the different requirements for your medications:
Wegovy®: This medication is now delivered without ice packs as it is stable at temperatures up to 30°C for the delivery period. Once received, unopened pens should be placed in the fridge (2°C–8°C). After the first use, you can keep the pen in the fridge or at room temperature (below 30°C) for up to 6 weeks.
Mounjaro®: This medication is still shipped with ice packs. It should be kept in the fridge (2°C–8°C) until its first use, and it must be discarded 30 days after that first dose.
Key Takeaway
Residual liquid in your pen after four doses is normal and expected.
Do not attempt to inject the remaining liquid.
Mounjaro pens expire 30 days after first use; Wegovy pens expire 6 weeks (42 days) after first use.
Always dispose of your pens and needles in a designated sharps bin.
If you still need help after reviewing the information above, additional assistance is available.