Around 80,000 prescriptions for liothyronine are given out each year.
Following its investigation into the pricing of the drug, the CMA found that the company had charged the NHS more than £34 million a year ago, which had increased from £600,000 in 2006.
But he stressed that the findings are provisional, with no definitive decision that there has been a breach of competition law.
Concordia said that it "does not believe competition law has been infringed".
THE SILENT KILLER Pancreatic cancer is one of the deadliest forms of the disease - but do YOU know the signs to watch for? It ratcheted up the price of its liothyronine drug, used to treat patients with underactive thyroids, by 6,000pc.
Actavis instead supplied Concordia with a fixed supply of its own 10mg tablets for a very low price for Concordia to resell in the United Kingdom, thus retaining its position of sole supplier in the country during most of the period, when the cost of the drug to the NHS rose from £49 to £88 per pack.
'We allege that Concordia used its market dominance in the supply of liothyronine tablets to do exactly that'. "Over that time, significant investment has been made in this medicine to ensure its continued availability for patients in the United Kingdom, to the specifications required by the Medicines and Healthcare products Regulatory Agency in the United Kingdom", the firm noted.
"We will review the CMA's preliminary position, as set out in its Statement of Objections, and we will be responding to it in detail". The watchdog found Actavis UK put up the price of generic 10mg tablets from 70p a pack in April 2008 to £88 per pack by March 2016. The CMA is pursuing another seven investigations into several companies in relation to drug pricing and competition issues. Once a drug goes generic, prices are usually driven down due to competition.
It also fined a group of pharma companies a total of £45m in relation to antidepressant paroxetine - but both these decisions are under appeal. The price of melphalan in the United Kingdom went up from 55p for 2mg in 2011 to £1.82 in 2016, a rise of 230 per cent.
The company is the latest to be accused of the ugly practice of price gouging. The CMA can levy a fine of up to 10% of a company's worldwide annual turnover if an infringement is found to have occurred.
The CMA recently went after Pfizer Inc. and its drug distributor Flynn Pharma for a similar breach, which resulted in a record fine of almost £90 million (about $113 million) for charging "excessive and unfair prices". We fully support the CMA in taking action in cases of proven abuse of market power.