The Competition and Markets Authority (CMA) has provisionally accused four anti-depressant suppliers: Alissa, Lexon, King and Auden Mckenzie of breaking the law and engaging in anti-competitive conduct.

The authority accused competitors King and Auden Mckenzie of sharing out between them the supply of nortriptyline to a large pharmaceutical wholesaler.

The CMA provisionally found that in 2014, the two companies agreed Auden Mckenzie would supply only 10mg nortriptyline tablets and King would supply only 25mg nortriptyline tablets, as well as agreeing to fix the quantities and the prices of supply.

The companies King, Alissa and Lexon have also been accused of exchanging commercially sensitive information, including information about prices, volumes and entry plans, to try to keep nortriptyline prices high.

Nortriptyline is prescribed by the NHS and relied on by thousands of patients every month to relieve the symptoms of depression, with NHS spending on the drug peaking at £38 million in 2015.

“If pharmaceutical companies get together to restrict competition for the supply of a drug, this can lead to the NHS – and ultimately the UK taxpayer – paying over the odds for what are often essential medical treatments,” explained Geoff Steadman, director of Antitrust at the CMA.

He continued, “We expect drug suppliers to abide by competition law so that the NHS is not denied the opportunity of benefitting from lower prices for medicines.”

This is just the CMA’s provisional finding and the companies now have the chance to make representations to the CMA before it reaches a final decision.