Why You Should Never Split or Share a Mounjaro Pen

In recent months, injectable weight-loss medications like Mounjaro (tirzepatide) have grown in popularity. But with rising demand comes a rise in unsafe practices, including a concerning trend of splitting or “sharing” pens.

Mounjaro is a prescription-only medication designed to be used as a sealed, sterile, single-patient device. It is carefully manufactured to deliver a specific, pre-calibrated dose for the individual it was prescribed for. Once that pen is opened, any attempt to share, divide, or “save” the remaining dose introduces serious risks, both medical and legal.

One of the key dangers lies in how the medicine itself is affected. Tirzepatide is a large, delicate molecule. When exposed to air, light, or temperature changes, as happens when a pen is opened and stored incorrectly, the drug can degrade. The remaining liquid may no longer be effective or reliable. What may appear to be a valid dose could in fact be compromised, reducing efficacy or altering how the body responds.

Another major concern is infection. These pens are sterile and designed for single-patient use. Drawing medication out manually, storing it elsewhere, or injecting from a pen that has already been opened can introduce bacteria or fungi into the solution. Patients have developed skin infections, abscesses, and even serious bloodstream infections from reusing or improperly splitting injectable medications. This is not theoretical, hospitalisations have occurred.

Equally important is the legal and clinical framework. Mounjaro is only legal when prescribed by a qualified healthcare provider to a named patient following a full medical assessment. Sharing a pen with a friend, family member, or partner is dangerous and prohibited. Without clinical review, there is no way to screen for contraindications, manage interactions with other medications, or properly monitor side effects. Tragically, there has already been at least one reported death in the UK linked to unsafe weight-loss injections administered without medical supervision.

Finally, it is not legal for a clinic or individual to sell “just one dose” by extracting part of a pen. This violates the UK’s prescribing and pharmacy regulations and places patients at risk of harm.

At Tower Hill Clinic, we take patient safety seriously. We provide full clinical assessment, legal prescribing, and structured follow-up care. If you are considering tirzepatide or other metabolic treatments, always seek proper medical guidance. Improvising with prescription medication is not self-care. It’s a shortcut to risk.