This study estimates how out-of-pocket drug costs could change for vulnerable populations (racial and ethnic minorities, the near-poor, and seniors with a greater burden of chronic conditions) who qualify for the standard Medicare drug benefit. Although the new benefit might be associated with modest-to-moderate declines in out-of-pocket spending for seniors who do not qualify for subsidies, the savings might not be shared equitably and therefore might not reduce financial barriers to medication use for these populations.