In a statement, Eli Lilly said: "The UK was one of the first countries where Lilly launched Mounjaro, and our priority was to bring it to patients as quickly as possible during a time of limited availability.
"At launch, Lilly agreed to a UK list price that is significantly below the European average to prevent delays in NHS availability.
"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."
Dr Leyla Hannbeck, head of the Independent Pharmacies Association, said she was "shocked and very disappointed" by the price rise.
"This is a real blow to patients at a time when more and more people, worried about their weight, are turning to jabs.
"It is vital that patients who are already taking Mounjaro talk to their local pharmacy before they take any action.
"Those patients considering weight-loss jabs should also not be put off as Mounjaro is not the only option. Local pharmacies are best placed to offer vital advice about the range of treatments available," Dr Hannbeck added.
Dr Sophie Dix head of medical affairs for online pharmacy Medexpress, and a former employee of Eli Lilly, told the BBC's Today Programme her firm was still trying to work out how much of the price rise would be passed on to customers.
The "absolute worst-case scenario" would be if customers turned to the blackmarket to source weight loss drugs, said Dr Dix.
"There are so many things that can go wrong with that. We always encourage patients to ensure that they are discussing their options with their provider rather than looking to other sources."