REVEALED: Date that new reduced size Mounjaro pens will be rolled out – as Eli Lilly clamps down on ‘golden dose’ hack
A date has been set for the rollout of the redesigned Mounjaro KwikPens in the UK, killing off the controversial ‘golden dose’ once and for all.
The change means some Mounjaro users will soon receive less medication for the same cost.
The pre-filled injection pens are currently 3ml in size and designed to deliver a fixed weekly dose of the drug, typically lasting four weeks.
However, a small amount of medication is often left in the pen after the fourth injection.
Some patients have taken advantage of this leftover liquid – a practice dubbed the ‘golden dose’ – by drawing it out with a syringe to use for an additional injection.
The redesigned pens will reduce the amount of residual medication, effectively preventing users from extracting a fifth dose.
Manufacturer Eli Lilly confirmed the modified KwikPen is expected to become available in the UK from April 2026.
The company said the device has been updated to minimise leftover medicine and make it easier for users to see when the pen has delivered its final dose and should be discarded.
The pre-filled injection pens are currently 3ml in size and designed to deliver a fixed amount of the drug once a week, typically over four weeks
‘The modified Mounjaro KwikPen continues to contain four fixed doses of medicine, along with a small additional amount to allow users to prime the pen before injection,’ an Eli Lilly spokesperson said.
‘In accordance with the Instructions for Use, the KwikPen should be disposed of after four doses, and the small amount of residual medicine should not be used.’
Existing stock of the current KwikPen will continue to be supplied until it runs out, meaning both versions will be available in the market for a transitional period.
While the updated pen functions in the same way as the original device, it includes several visual and structural changes.
The plunger now sits further down the cartridge when the pen is unused, and a new internal component has been added behind it to extend its length. After the fourth injection, the plunger will sit close to the end of the pen – clearly signalling that it is empty and ready to be discarded.
Health officials have repeatedly warned patients against attempting to extract a so-called golden dose, saying the practice could lead to injury or infection.
The change also comes amid rising costs. From September 1, 2025, Eli Lilly increased the UK private wholesale price of Mounjaro by up to 170 per cent, raising the cost of the highest dose from roughly £122 to £330 per month.
In September 2025 when the smaller pre-filled injection pens were first announced, it sparked ‘Covid-like panic buying’ with users boasting online of buying months worth of injection pens, to avoid having to pay the new price.
Mounjaro users took to social media to share tips on how to ‘golden dose’, in an attempt to make the pens last longer on their new price.
An Eli Lilly spokesperson told the Daily Mail at the time: ‘A modified KwikPen will be made available globally.
‘While the modified KwikPen has been approved in the UK, the timelines for availability are yet to be determined.
‘The initial Mounjaro KwikPen and the modified Mounjaro KwikPen both contain the volume of solution necessary for priming before each injection and the delivery of four doses (one dose given weekly).
‘The KwikPen has been modified to reduce the amount of leftover medicine that remains in the KwikPen after four doses have been administered.’
Each Mounjaro pen contains 3ml of liquid, and each dose uses 0.6ml—just enough for four, accurate, pre–measured doses of Mounjaro.
The above image shows there is still liquid left over in the pen after the prescribed four doses – which many say is enough for a fifth
By getting five doses out of each pen, regular users could save around £615 a year.
Currently Pharmacy2U, the UK’s largest online pharmacy, has the strongest Mounjaro pen- 15mg- listed at £299.99, a huge leap from its previous price of £180.
Furious users labelled Eli Lilly’s decision a ‘kick in the teeth’ and claimed they would still try to ‘golden dose’.
In one Reddit forum, a user wrote: ‘Wow. This company are truly the gift that keeps on giving.’
Another said: ‘I think they’ll phase the release so it will be a random chance whether you get the old pen or the new one which will Indirectly make stock piling risky.’
Meanwhile a third user said: ‘They really have shafted us all and were likely making a very good profit before the changes.’
Others claimed it wouldn’t stop them from trying to extract whatever was left over.
‘Maybe half a dose left over so combining two pens with leftover for a full dose. The new golden 9th,’ one said.
Similar to microdosing, which sees users try and inject a smaller than normal Mounjaro dose, health chiefs have also repeatedly urged patients against trying the ‘golden dose’ hack.
Dr Alison Cave, chief safety officer of the MHRA, said: ‘People should follow the dosing directions provided by their healthcare provider when prescribed weight–loss medicines and use as directed in the patient information leaflet.
‘Medicines are approved according to strict dosage guidelines.
‘Failure to adhere with these guidelines, such as tampering with pre–dosed injection pens, could harm your health or cause personal injury.’
Professor Penny Ward, a pharmaceutical expert at King’s College London, also told the Daily Mail: ‘People are reading these tips on online forums and being tempted to use them to save money.
‘But they’re risking serious side effects from overdosing by doing this — as well as the potential to develop a life-threatening infection. It’s not a good idea at all.
‘These injections contain a slight overfill to ensure the full recommended dose is delivered each time.
‘But by drawing this out with a separate syringe and using it as a so-called fifth dose, you’re exposing yourself to serious risk of infection.
‘The pens are sterile when dispensed, but once they’ve been used, they’re no longer sterile.
‘That means using leftover liquid to inject into the skin could introduce harmful bacteria.
‘This can lead to an abscess—a painful build-up of pus—and if left untreated, potentially progress to sepsis, a life-threatening condition where the body’s organs begin to shut down.’
Under official guidelines, only patients who have a body mass index (BMI) of over 40 and weight-related health problems like high blood pressure, type 2 diabetes and obstructive sleep apnoea, should be prescribed Mounjaro on the NHS.
But tens of thousands are believed to be using them privately.
It comes as a damning analysis last week revealed thousands of people are missing out on Mounjaro on the NHS because of a ‘postcode lottery’ of NHS provision.
In 2024, health chiefs announced millions of obese patients would receive Mounjaro – which helps slimmers shed up to a fifth of their bodyweight – on the health service over a phased 12 year rollout.
But since the rollout began in June 2025, less than half of the commissioning bodies in England have even started prescribing the drug, analysis by the British Medical Journal found.
Weight-related illness costs the economy £74billion a year, with people who are overweight at increased risk of heart disease, cancer and type 2 diabetes.
Two in three Britons are classed as overweight or obese and NHS figures show people now weigh about a stone more than 30 years ago.
