Pharmaceutical companies are warning against tampering with pens and experts have outlined the major risks.
While the KwikPen is not reducing in size, the volume of the medicine inside will be reduced in the future(Image: Peter Dazeley via Getty Images)
Mounjaro, the brand name for tirzepatide, is a drug that lowers blood sugar levels but has rose to prominence in the last year for its use as an injectable weight loss medication that has seen overweight Brits lose tens of pounds.
This week, the Record reported that Mounjaro manufacturer Eli Lilly is reducing the amount in its injection pens, removing the so-called ‘golden dose’. This means users who have been able to squeeze an extra dose from the leftover medicine in each syringe will no longer be able to get five weeks out of their monthly prescription.
The Mounjaro pen currently has an excess of medication to ensure proper priming of the needle before administration and to make sure there is enough for the four doses following this each time.
Instead of discarding this, people on social media have been encouraging individuals to try out the “fifth dose” to get more for their money. However, pharmacists have warned that taking this dose can be “dangerous”.
To keep you clued up, the experts at Chemist4U sharing the risks of taking the “golden dose” in Mounjaro pens.
What are risks of taking the ‘golden dose’?
Mounjaro has been recommended to help dangerously obese people lose weight on the NHS(Image: Peter Dazeley via Getty Images)Overdosing and pancreatic issues
The “5th dose” or “golden dose” refers to a self-added dose to the pen’s standard four doses. It’s believed that this extra amount of liquid is added to ensure there is sufficient excess fluid to prime the pen.
The extra liquid is not a measured or intended dose, and its volume may be inconsistent, which can lead to under dosing or overdosing and even the risk of injecting expired medication.
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Trying to extract a fifth dose can also damage the pen, increase the risk of side effects, and disrupt your treatment plan. Always use your pen exactly as prescribed and discard the pen after four doses, even if some liquid remains.
“The higher the dose, the higher the risk of gastrointestinal reactions such as nausea, vomiting, or diarrhoea as well as the potential for an increased risk of pancreatic issues,” said Ayesha Bashir, Prescribing Pharmacist at Chemist4U.
Sterility and performance
The Kwikpen used to administer Mounjaro must be discarded after the four doses, or after a period of 30 days after the first dose is used, as per manufacturer instructions.
Continuing use beyond that may present unknown sterility and performance risks , including potential health issues.
If a user suffers side effects, dosing failure, or infection after using a pen beyond its approved use period, Eli Lilly may decline responsibility, which could also undermine the legitimacy of any reported adverse event or claim.
Risk of bacterial contamination and infection
A small amount of medication remains in the pen after the final injection (Image: Peter Dazeley 2025)
Opening the Mounjaro KwikPen and extracting medication with a syringe can compromise the pen’s sterile interior and introduce the risk of bacterial contamination or infection.
A recent lab study of insulin vials from diabetic patients found that 6.2 per cent of vials were contaminated with bacteria due to syringe reuse and poor storage conditions.
This shows how even non-clinical, household-level handling can introduce pathogens when sterile needles are tampered with or reused inappropriately.
Misusing or ‘stretching’ pens can spark side effects
Jason Murphy, Head of Pharmacy and weight loss injections expert at Chemist4U, said: “People will experience more periods of hunger, resulting in overeating and hampered results.
“Also, when they next inject, their body will have to get used to a higher dose again, leading to potential side effects such as prolonged nausea. ”
Jason said professionals and regulators are aware of the growing trend of Mounjaro KwikPen misuse and Medicines and Healthcare products Regulatory Agency (MHR) are monitoring it.