The US Department of Justice announced Tuesday that they were bringing suit against drugmaker Mallinckrodt for defrauding Medicaid. The suit stems from an increase in the price of one of their drugs, Acthar, which was raised from $50 a vial to nearly $40,000 a vial, according to the complaint.

When the price of a drug increases dramatically the company is supposed to pay back to Medicaid, in rebates, the price above the inflation rate. The rate is determined by the year the drug was brought to the market or the 1990 Rate of Inflation. The company had been paying rebate rates as if the drug was first introduced in 2013, which made the money owed for inflation very low. In reality, the complaint claims the drug was introduced in 1950 and should have been paying the 1990 Rate of Inflation, which would mean almost all of the money it cost should have been paid back to Medicaid.

The US is seeking damages in the amount owed by Mallinckrodt in rebates.