How to get the remaining Mounjaro out of the pen — and what the guidance actually says

What the SmPC and prescribing guidance say about pen residue

The Mounjaro KwikPen is engineered to deliver four pre-set subcutaneous doses from a single cartridge. Once the fourth dose has been given, the pen locks. At that point, a small amount of fluid almost always remains visible in the cartridge window. This is not a dosing error or a manufacturing fault. Eli Lilly's design intentionally includes a dead-volume buffer so that each of the four measured doses is delivered in full, the residual liquid is the safety margin that makes that precision possible.

The eMC's Mounjaro prescribing information does not describe any approved method for extracting remaining contents after a pen has delivered its final dose, because there is no such method within the licensed use of the product. If you are curious about what is physically possible with the device, we have a guide on how to get an extra dose out of a Mounjaro pen, which explains why improvising (by inverting the pen, applying pressure to the plunger, or trying to draw liquid into a syringe) would mean administering an unknown amount of tirzepatide outside the conditions under which it was authorised and studied.

That matters clinically. Tirzepatide is a dual GIP and GLP-1 receptor agonist; dose precision is built into the titration schedule precisely because the side-effect profile, particularly gastrointestinal effects, is closely linked to how much is injected and how quickly. The NHS medicines page for tirzepatide recommends following your prescriber's instructions and the leaflet, and reporting unexpected experiences to your care team.

If the pen is not delivering properly before the final dose

A different situation (one our prescribers hear about reasonably often) is a pen that seems not to have injected a full dose mid-course: the plunger felt stiff, the injection site bled more than usual, or the dose counter did not move. That is separate from residual fluid after a completed pen, and it is worth reporting.

The right step is to contact your prescribing service, not to attempt a repeat injection from the same pen. The reason is straightforward: you cannot know from external signs whether a full dose was delivered subcutaneously or not, and a prescriber needs to advise you before you take any further action. If you use nume for your treatment, our aftercare team is available seven days a week precisely for moments like this, contact us and a prescriber can review your situation the same day.

For practical technique questions around injection (angle, site rotation, needle changes) our FAQs page covers the most common ones, and our prescribers are always the right point of call for anything beyond them.

The safe, legal route to Mounjaro in the UK

Mounjaro is a Prescription-Only Medicine. The only lawful route to it in the UK is a prescription issued following a clinical assessment by an authorised prescriber. That is not a bureaucratic detail; it is the mechanism that keeps you on the right dose, with the right monitoring, with a genuine product from the licensed supply chain.

Counterfeit weight-loss pens are a real problem. The MHRA has warned publicly about fake pens sold online and via social media, and enforcement action through 2025 resulted in approximately 20 million doses of illegally traded medicines (around £45m street value) being seized, including the first illicit UK site producing counterfeit tirzepatide pens. You can report a suspect seller via the MHRA's Yellow Card scheme. Any seller offering these medicines without a clinical assessment is a red flag.

Before placing an order with any online pharmacy, check its GPhC registration at the GPhC register, nume's premises registration number is 9012878. You can verify it in under a minute.

At nume, the process is straightforward: you complete a free consultation, a GPhC-registered Independent Prescriber reviews it the same day, and if you're clinically suitable your treatment is dispatched the same day, arriving free the next working day via DPD. Monday orders before 12pm mean treatment can reach you Tuesday morning, which matters if your injection day falls early in the week or you have a bank holiday coming up. You can read more about buying Mounjaro through a regulated UK pharmacy, or explore the full Mounjaro treatment overview to understand what starting looks like.

Who may be eligible, and what a prescriber assesses

Mounjaro is licensed for adults with a BMI of 30 or above, or those with a BMI of 27 or above alongside at least one weight-related condition such as high blood pressure, high cholesterol, type 2 diabetes, or obstructive sleep apnoea. Lower BMI thresholds apply for some ethnic backgrounds under UK guidance. BMI alone never determines outcome, the prescriber's clinical picture includes your full health history, current medicines, and any contraindications.

Under-18s are not covered by the licence. Mounjaro is not recommended during pregnancy, while breastfeeding, or when actively trying to conceive. Anyone on oral contraceptives should know that tirzepatide may affect pill absorption, particularly in the first four weeks of treatment and after each dose increase, adding a non-oral method of contraception during those windows is the standard recommendation.

If you are already mid-treatment with another provider and want to switch to nume, our prescribers can review your dose history and continue your titration appropriately. Some patients also ask about managing their pen across a titration schedule, and if that applies to you, our guides on how to get 2.5mg out of a 5mg Mounjaro pen and how to get 5 doses out of a Mounjaro pen explain what the device does and does not allow. See our guidance on getting the most from your Mounjaro treatment, and if you have questions about how the dose schedule works, our weight-loss treatment overview is a good starting point before your consultation.