PDP stands for Prescription Drug Plan. It’s a stand-alone insurance plan that covers prescription medications under Medicare Part D. PDPs are sold by private insurance companies approved by Medicare, and they’re optional. You’d typically pair one with Original Medicare (Part A and Part B) to add drug coverage that Original Medicare doesn’t include on its own.
How a PDP Works
A PDP covers a specific list of prescription drugs called a formulary. Each plan organizes its formulary into tiers that determine what you pay at the pharmacy. Most plans use a structure like this:
- Tier 1: Generic drugs with the lowest copayment
- Tier 2: Preferred brand-name drugs with a medium copayment
- Tier 3: Non-preferred brand-name drugs with a higher copayment
- Specialty tier: Very high-cost drugs with the highest copayment
Not every PDP covers the same drugs, and the tier placement can vary between plans. Before enrolling, you can check whether your medications are on a plan’s formulary and which tier they fall under. This is one of the most important steps in choosing the right PDP, since it directly affects what you’ll pay each month at the pharmacy.
PDP vs. Medicare Advantage Drug Coverage
There are two ways to get Part D drug coverage. A stand-alone PDP pairs with Original Medicare, while a Medicare Advantage Prescription Drug plan (MA-PD) bundles drug coverage into a broader Medicare Advantage plan that also handles your hospital and medical coverage.
The financial structure behind these two options differs in ways that affect premiums and benefits. MA-PD plans have access to additional funding through rebates from the Medicare Advantage side, which they can use to lower premiums or enhance drug benefits. Stand-alone PDPs don’t have that extra funding source, so their premiums reflect the full expected cost of drug coverage. According to MedPAC, PDPs are more likely to incur financial losses compared to MA-PD plans because of this structural difference.
You can’t enroll in both. If you have Original Medicare and want drug coverage, you choose a PDP. If you switch to a Medicare Advantage plan that includes drug coverage, your stand-alone PDP would end.
Who Can Enroll
To join a PDP, you need to have Medicare Part A, Part B, or both. You also need to live in the plan’s service area and be a U.S. citizen or lawfully present in the country. Enrollment must happen during a valid election period.
The main enrollment windows are:
- Initial Enrollment Period: A seven-month window that starts three months before you first get Medicare and ends three months after
- Open Enrollment Period: October 15 through December 7 each year, when you can join, switch, or drop a plan for the following year
- Medicare Advantage Open Enrollment Period: January 1 through March 31, when someone in a Medicare Advantage plan can switch back to Original Medicare and pick up a stand-alone PDP
The Late Enrollment Penalty
If you don’t sign up for a PDP when you’re first eligible and go 63 or more consecutive days without what Medicare considers “creditable” drug coverage (coverage at least as good as a standard Part D plan), you’ll face a permanent penalty. The penalty adds 1% of the national base beneficiary premium for every month you went without coverage. In 2026, the national base beneficiary premium is $38.99.
So if you went 14 months without creditable coverage, your penalty would be 14% of $38.99, which rounds to $5.50 per month. That amount gets added to your plan’s monthly premium for as long as you have Part D coverage, and it can increase each year as the base premium changes.
The $2,000 Out-of-Pocket Cap
Starting in 2025, a major redesign of Part D took effect under the Inflation Reduction Act. The most significant change: your total out-of-pocket spending on prescription drugs is now capped at $2,000 per year. Once you hit that threshold, you pay nothing more for covered drugs for the rest of the year.
This redesign also eliminated the coverage gap, commonly known as the “donut hole,” the phase where people previously had to pay a larger share of their drug costs after initial coverage ran out. The Part D benefit now has three straightforward phases: the annual deductible, initial coverage, and catastrophic coverage (where the $2,000 cap kicks in and your costs drop to zero).
Financial Help Through Extra Help
If your income and savings are limited, you may qualify for Medicare’s Extra Help program (also called the Low Income Subsidy), which helps pay Part D premiums, deductibles, and copayments. For 2025, the income limits are $23,475 for an individual and $31,725 for a married couple in most states. Resource limits are $17,600 for individuals and $35,130 for couples.
Resources include cash, bank accounts, retirement accounts, stocks, bonds, and real estate beyond your primary home. They don’t include your house, one car, household items, furniture, or up to $1,500 set aside for burial expenses. Income counts wages, Social Security benefits, pensions, and veterans benefits, but excludes things like SNAP benefits, home energy assistance, and housing assistance. Even if your income exceeds the listed limits, you may still qualify if you support other family members living with you.
Choosing a PDP
CMS rates every PDP on a 1-to-5 star scale based on up to 12 quality and performance measures. Star ratings give you a quick way to compare plans, but the most practical factors are whether the plan covers your specific medications, which pharmacies are in network, and what your total annual costs will look like given your prescriptions. Two plans with the same monthly premium can cost very different amounts over a year depending on how they tier your drugs. Medicare’s Plan Finder tool on medicare.gov lets you enter your medications and compare estimated annual costs side by side.