Formulary tier changes mid-year force patients to switch stable medications

Health insurers reclassify drugs between formulary tiers mid-plan-year, moving a patient's stable medication from Tier 2 ($30 copay) to Tier 4 ($150 copay) or off-formulary entirely with no clinical justification. A patient who has been stable on a specific antidepressant for two years is suddenly forced to either pay 5x more or switch to a "preferred" alternative that may cause different side effects and require weeks of dose titration. Insurers are allowed to do this because CMS only locks formularies for Medicare Part D mid-year; commercial plans face no such restriction. Pharmacy benefit managers (PBMs) drive these changes to capture rebate revenue from competing drug manufacturers, meaning the tier assignment reflects financial deals, not clinical efficacy.