A prescription drug plan is a type of insurance that helps cover the cost of your medications. Most commonly associated with Medicare Part D, these plans pay a portion of what you’d otherwise spend out of pocket on prescriptions, in exchange for a monthly premium. They’re offered by private insurance companies, and while the specifics vary from plan to plan, they all follow a general structure: you pay into the plan, the plan maintains a list of drugs it covers, and your costs at the pharmacy depend on what tier your medication falls into.
How Prescription Drug Plans Work
Every prescription drug plan has a formulary, which is simply the list of medications the plan agrees to cover. Drugs on the formulary are organized into tiers, and the tier determines how much you pay. A typical plan uses four tiers:
- Tier 1 (lowest cost): Most generic drugs
- Tier 2 (medium cost): Preferred brand-name drugs
- Tier 3 (higher cost): Non-preferred brand-name drugs
- Specialty tier (highest cost): Very high-cost drugs, often for complex conditions
When you fill a prescription, you’ll pay either a copay or coinsurance. A copay is a flat fee, like $15 for a generic drug. Coinsurance is a percentage of the drug’s cost, so if your medication costs $200 and your coinsurance is 25%, you pay $50. Plans typically use copays for lower tiers and coinsurance for specialty medications, which is where costs can climb quickly.
Not every drug on the formulary is available without restrictions. Plans can require prior authorization, meaning your doctor must get approval from the insurer before the plan will cover a particular medication. Some plans also use step therapy, which requires you to try a less expensive drug first and only move to a costlier option if the first one doesn’t work. Quantity limits cap how much of a medication you can get in a given time period.
Medicare Part D: The Most Common Version
If you’re on Medicare, prescription drug coverage comes through Part D. You can get it in two ways: as a standalone drug plan that you add to Original Medicare (Parts A and B), or bundled into a Medicare Advantage plan (Part C), which wraps medical and drug coverage into a single plan from a private insurer. Either way, the drug benefit follows the same basic Part D rules.
In 2025, Part D coverage moves through distinct stages. First, you pay 100% of your drug costs until you’ve spent $590, which is the annual deductible. After that, you enter the initial coverage stage, where you typically pay about 25% of your drug costs and the plan covers the rest. This continues until your total out-of-pocket spending hits $2,000 for the year. Once you cross that threshold, catastrophic coverage kicks in and the plan covers all remaining drug costs for the rest of the year.
That $2,000 cap is a major change. The Inflation Reduction Act restructured Part D benefits starting in 2025, eliminating the old “donut hole,” a coverage gap where people with high drug costs were left paying a much larger share. Previously, annual out-of-pocket costs could reach $7,000 or more. The new cap is a significant reduction for anyone taking expensive medications.
What It Costs Each Month
Every Part D plan charges a monthly premium, and the amount varies by plan and region. You’re paying for the insurance itself, separate from what you spend at the pharmacy. Plans with lower premiums often have higher copays or coinsurance, and vice versa, so the cheapest monthly premium isn’t always the best deal if you take multiple medications.
If you don’t sign up for a drug plan when you’re first eligible and you don’t have other qualifying coverage, you’ll face a late enrollment penalty. The penalty is calculated as 1% of the national base premium for each month you went without creditable coverage. That extra charge gets added to your monthly premium permanently, so the longer you wait, the more you pay for the rest of the time you’re enrolled in Part D.
What “Creditable Coverage” Means
Creditable coverage is a term that matters if you have drug coverage from somewhere other than Medicare, like an employer or union plan. It means the coverage is expected to pay, on average, at least as much as a standard Medicare Part D plan. If your employer plan is creditable, you can delay enrolling in Part D without penalty.
Employers are required to notify Medicare-eligible employees in writing each year, before October 15, whether their drug plan counts as creditable. If you receive a notice saying your coverage is not creditable and you choose to keep it instead of enrolling in Part D, you’ll accumulate those penalty months. Holding onto that letter is important if you ever need to prove you had qualifying coverage.
Standalone Plans vs. Medicare Advantage
Choosing between a standalone Part D plan and a Medicare Advantage plan with drug coverage depends on how you want your overall Medicare to work. With Original Medicare, you pick your own doctors, see specialists without referrals, and add a standalone drug plan on top. You might also carry a Medigap (supplemental) policy to help with hospital and doctor visit costs.
Medicare Advantage bundles everything. Your hospital coverage, doctor visits, and prescriptions all come through one plan, often with extras like dental or vision. The tradeoff is that most Advantage plans use provider networks, so your choice of doctors and hospitals may be more limited. Drug formularies can also differ between the two types, so the plan that covers your specific medications at the lowest cost may not be the one with the lowest premium.
Financial Help for Lower Incomes
Medicare’s Extra Help program (also called the Low Income Subsidy) reduces Part D costs for people with limited income and savings. In 2025, you may qualify if your annual income is below $23,475 as an individual or $31,725 as a married couple. Resource limits are $17,600 for individuals and $35,130 for couples. Resources include savings, stocks, and bonds, but not your home or car.
If you qualify, Extra Help can lower or eliminate your premium, deductible, and copays. Even if your income is slightly above these limits, you may still be eligible if you support other family members in your household. Applying is free through Social Security, and there’s no downside to checking whether you qualify.
Prescription Drug Plans Outside Medicare
Medicare Part D gets the most attention, but prescription drug coverage also exists in employer-sponsored health insurance, Affordable Care Act marketplace plans, and Medicaid. In employer and marketplace plans, drug coverage is built into the overall health plan rather than sold separately. These plans use similar structures: formularies, tiers, copays, and coinsurance. The Affordable Care Act requires marketplace plans to cover prescription drugs as one of ten essential health benefits, though which specific medications are covered varies by insurer.
Medicaid provides drug coverage for people with very low incomes, and while states aren’t required to include prescription drugs, all currently do. Medicaid drug benefits typically have minimal or no cost sharing, though formularies can be more restrictive than what you’d find in a commercial plan.