The Inflation Reduction Act requires drug manufacturers to pay a rebate to the federal government if prices for single-source drugs and biologicals covered under Medicare Part B and nearly all covered drugs under Part D increase faster than the rate of inflation (CPI-U). Price changes will be measured based on the average sales price for Part B drugs and the average manufacturer price for Part D drugs. If price increases are higher than inflation, manufacturers will be required to pay the difference in the form of a rebate to Medicare. The rebate amount is equal to the total number of units sold in Medicare multiplied by the amount, if any, by which a drug’s price in a given year exceeds the inflation-adjusted price. For Part B drugs with price increases greater than inflation, beneficiary coinsurance will be based on 20% of the drug’s lower inflation-adjusted price. The base year for measuring cumulative price changes relative to inflation is 2021.