Original Medicare doesn’t cover prescription drugs. Part D fills that gap — either as a standalone plan alongside Original Medicare/Medigap, or bundled into a Medicare Advantage plan.
Each Part D plan has a formulary — a list of covered drugs organized into cost tiers — along with its own network of pharmacies. Two plans can cover the same medication at very different costs, which is why comparing your specific prescription list against each available plan matters more than picking the plan with the lowest premium alone.
Thanks to the Inflation Reduction Act, Medicare Part D now includes a hard annual cap on what you pay out of pocket for covered prescriptions — $2,100 in 2026. Once you hit that cap (from deductibles, copays, and coinsurance combined), your plan covers 100% of covered drug costs for the rest of the year. This cap does not include your monthly premium.
If you go 63 days or more without Part D or other "creditable" drug coverage after becoming eligible, you may face a late enrollment penalty added to your premium for as long as you have Part D. Enrolling on time — even in a low-cost plan — helps you avoid this.
