Pharmaceutical giant Eli Lilly has announced substantial increases to Mounjaro's UK list price, with rises reaching 170 per cent for certain doses.
The weight-loss medication, used by approximately 1.5 million Britons, will see its highest-dose monthly cost surge from £122 to £330.
The price hike impacts private purchasers, who represent roughly 90 per cent of UK users accessing these treatments through online services and high street pharmacies.
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Eli Lilly confirmed that the "necessary pricing adjustments" will be made by September 1.
As part of an agreement with the UK Government, NHS patients remain protected from the increase due to previously negotiated discounted rates.
The injectable treatment, administered weekly, helps patients achieve weight reduction of up to 20 per cent by suppressing appetite.
Eli Lilly justified the adjustment by stating the medication had been marketed in Britain at rates "significantly below" those in other European nations, to "prevent delays in NHS availability".
Mounjaro is used by approximately 1.5 million Britons
| GETTYThe pharmaceutical firm cited environmental shifts and fresh clinical data supporting Mounjaro's effectiveness as reasons for the revision.
"With changes in the environment and new clinical evidence supporting the value of Mounjaro, we are now aligning the list price more consistently to ensure fair global contributions to the cost of innovation," the company stated.
The pharmaceutical company added: "Lilly supports the administration’s goal of keeping the United States the world's leading destination for biopharmaceutical research and manufacturing, and the objective of more fairly sharing the costs of breakthrough medical research across developed countries."
But some experts have expressed alarm at the announcement. Dr Leyla Hannbeck from the Independent Pharmacies Association described herself as "shocked and very disappointed" by the increase, according to the BBC.
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The Mounjaro price hike impacts private purchasers
| GETTYShe called it "a real blow" to more and more patients who are turning to jabs for weight loss solutions.
In a similar vein, medical professionals have warned about the potential dangers of seeking cheaper alternatives.
Speaking on the BBC's Today Programme, Dr Sophie Dix from online pharmacy Medexpress warned that the "absolute worst-case scenario" would involve customers "turning to the black market".
Dr Dix urged patients to discuss their options with their provider rather than seeking alternative sources.
The price revision occurs amid broader pharmaceutical pricing debates, particularly following US President Donald Trump's criticism of American drug costs.
Trump has proposed a "most favoured nation" pricing system linking US prices to international rates.
What is Mounjaro?
Mounjaro is a weekly injection containing tirzepatide that helps manage weight by making patients feel full for extended periods after eating.
The medication requires a prescription through specialist weight management services for eligible patients.
NHS access has initially been restricted to patients with the most severe obesity and multiple health complications, defined as the "highest clinical need".
Women planning pregnancy should avoid this treatment, as should breastfeeding mothers.