Increases are expected to mainly affect stand-alone Part D plans, not the drug coverage offered as part of Medicare Advantage, the private sector alternative to original Medicare...

Policy experts say premiums are likely to go up for several reasons, including increased use of some higher-cost prescription drugs; a law that capped out-of-pocket spending for enrollees; and changes in a program aimed at stabilizing price increases that the Trump administration has continued but made less generous.

Medicare Part D premiums are likely to go up next year. Here's why.