How to revive a tirzepatide pen that isn't flowing properly

Step 1, Before you do anything else, check the needle

The vast majority of "blocked" tirzepatide pens turn out to be needle problems. The Mounjaro KwikPen requires a fresh, compatible pen needle screwed on firmly before each injection. If the needle is cross-threaded, not fully seated, or was left on from a previous dose and has dried medication in the hub, the pen will push against resistance and appear not to work.

Remove the current needle by unscrewing it carefully. Dispose of it in a proper sharps container, never a household bin. Attach a new, unused needle from a sealed pack, turning it until it is snug. Then check the pen window: the liquid should look clear and colourless. Cloudiness, particles or discolouration mean the pen should not be used regardless of what else you do.

One practical thing worth knowing: the tirzepatide pen that arrives in your order (tracked by DPD, in plain unbranded packaging) already has its dose set and sealed. The needle is the only consumable you add. Getting that step right accounts for more "failed" pens than any other single cause, according to the instructions Eli Lilly publish for healthcare professionals.

Step 2, Prime the pen correctly before injecting

Priming removes air from the needle and confirms the pen is ready to deliver medication. With the new needle attached and the outer cap removed, hold the pen with the needle pointing upward. Press the injection button and watch for a small stream of liquid or a drop at the needle tip. If nothing appears on the first attempt, the Patient Information Leaflet advises trying the priming step again, but only a limited number of times as described in your specific leaflet, which you should read carefully before each first use of a new pen.

Do not skip priming because you are trying to conserve a dose. An unprimed pen may deliver air instead of medication, or an incomplete amount. The priming drop is small; it does not meaningfully reduce the dose that reaches you.

For a full visual walkthrough of the injection technique, our guide to using the tirzepatide pen covers each stage in sequence, including needle attachment and site rotation. If you are new to self-injection, reading that guide alongside your leaflet is time well spent.

Step 3, Confirm the pen was stored correctly

Temperature is the silent problem. Mounjaro KwikPens must be refrigerated at 2–8°C between uses. A pen that has been left on a worktop, in a warm car or near a radiator may have been exposed to temperatures outside that range for longer than the leaflet permits. The exact window (the number of hours or days a pen can safely spend at room temperature) is set out in the Patient Information Leaflet; always check that document rather than relying on memory or online guides, because the window applies cumulatively across the pen's lifetime, not just the most recent occasion it was out.

If you are not certain how long the pen was outside the fridge, the safest course is to contact our team before injecting. A prescriber can advise whether to use it or replace it. You can reach the aftercare team seven days a week. Attempting to use a heat-compromised pen is unlikely to cause harm in the way a contaminated medicine might, but it may mean you receive little or no active medication, undermining the point of the dose entirely.

The cost context is worth considering here. Eli Lilly raised UK list prices significantly from September 2025, as we've covered in detail. A wasted pen is a meaningful expense, which is exactly why working through this sequence carefully before discarding one makes sense, and why contacting your pharmacy before giving up is always the right move.

When to stop troubleshooting and get help

Some situations call for you to put the pen down and make contact rather than continuing. Stop immediately if: the pen shows visible damage to the cartridge window or casing; liquid is leaking from anywhere other than the needle tip during injection; the plunger moves with no resistance at all; or you have worked through priming twice and nothing flows.

Also stop if you have completed the injection but are not confident the full dose was delivered, for instance, if the pen seemed to stall partway through. The MHRA's Yellow Card scheme at yellowcard.mhra.gov.uk is the right place to report a suspected device defect, and doing so helps the regulator track pen quality across the UK.

At nume, every patient has access to prescriber support seven days a week. If you have a concern about your pen or your injection, you do not need to wait until Monday. The Mounjaro treatment page outlines what ongoing clinical support looks like through a private prescription. For broader questions about injection technique across the tirzepatide range, the tirzepatide injection hub is a useful next read.

If you are not yet on treatment and want to understand whether tirzepatide suits your situation, you can read what other patients have said about their tirzepatide injection experience before speaking to our prescribers, consultations are free and reviewed by a GPhC-registered prescriber, not an automated system.