Can my plan move a drug to a different tier mid-year?

Usually no. Most Part D plans are contractually restricted to tier moves only at plan-year resets (typically January 1). Mid-year tier changes require either contract amendment or specific carve-out language in the plan-PBM agreement.

There are limited exceptions: (1) a drug's generic becomes available mid-year and the plan can move from brand tier to generic tier; (2) FDA safety issues require restricting coverage; (3) the contract explicitly grants the plan tier-move authority mid-year.

This is one of the largest hidden frictions in pharmacy benefits: even when a savings opportunity becomes obvious mid-year, the plan often cannot capture it for 6-12 months. Plans renegotiating contracts should specifically demand mid-year tier-move authority on drugs with 10+ generic manufacturers as a contract provision.