Mounjaro users will soon be getting less for their money after drug manufacturer Eli Lily confirmed that a change to their KwikPens mean there will be less medicine in each pen.
This means that users who have been 'hacking' the pen to get an extra dose from the left over medicine in each syringe will no longer be able to make the monthly prescription last for five weeks rather than four.
Since Mounjaro became available in the UK last February, some patients have shared tips on social media claiming a small amount of medication remains in the pen after the final injection -- and that it can be salvaged and administered.
Dubbed the 'golden dose', the leftover liquid can, they suggest, be drawn out using an insulin syringe and needle, or the 'clicker' which measures each dose can be forced open, allowing the contents to be used for an additional jab.
By getting five doses out of each pen, regular users could save around £615 a year -- and that was before manufacturer Eli Lily announced the wholesale cost of the medicine would be increasing in price by 170 per cent.
Currently Pharmacy2U, the UK's largest online pharmacy, has the strongest Mounjaro pen -- 15mg -- listed at £314, a huge leap from its previous price of £180.
Eli Lilly, which makes the drug, announced that wholesale prices would more than double from September 1 -- with the highest dose rising from £122 to £330 a month.
Mid-range doses, such as the 5mg pen, were also set to jump from about £92 to £180.
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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
The move prompted slimmers to rush to stockpile months worth of Mounjaro after panic grew over its soaring cost.
Many users have justified investing hundreds of pounds on the life-changing drug because they can make it last for five weeks, reducing its weekly cost, or by taking a smaller 'micro-dosed' amount to make each pen last longer.
Each Mounjaro pen contains 3ml of liquid, and each dose uses 0.6ml -- just enough for four, accurate, pre-measured doses of Mounjaro.
But this leaves a small amount of liquid behind that a growing number of Mounjaro users are attempting to squeeze out, dubbed the 'golden dose'.
The leftover liquid, however, is not a bonus dose -- it's a deliberate overfill built into the pen to ensure complete delivery of each injection.
A spokesperson told the Daily Mail: '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).
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'The KwikPen has been modified to reduce the amount of leftover medicine that remains in the KwikPen after four doses have been administered.'
At least half a million NHS patients and some 15million patients in the US are now thought to be using weight-loss jabs, which can help patients lose up to 20 per cent of their body weight in just a few months.
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And the numbers using them privately are even higher.
Under official guidelines, only patients who have a body mass index (BMI) of over 35 and at least one weight-related health problem like high blood pressure, or those who have a BMI of 30 to 34.9 and meet the criteria for referral to a specialist weight management service, should be prescribed weight-loss jabs.
Reddit users who found out about the forthcoming change in the KwikPen were furious.
One commented: '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 one user said 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,' they said.