Medicare Part D — Prescription Drug Benefit

Medicare Part D is the federal program that pays for outpatient prescription drugs for Medicare beneficiaries — roughly 66 million Americans. Created by the Medicare Modernization Act of 2003 and administered by private insurance companies under CMS contract, Part D is one of the largest payers of prescription drugs in the world, covering more than $200 billion in drug spending annually. If you are on Medicare, Part D is almost certainly relevant to you: it determines which drugs are covered, how much you pay at the pharmacy counter, and whether you qualify for additional financial help.

Current Law (2026)

Legal Authority

• 42 U.S.C. § 1395w-101 — Eligibility, enrollment, and information: establishes who qualifies (all Medicare-eligible individuals), how enrollment works, and the information CMS must provide about plans
• 42 U.S.C. § 1395w-102 — Prescription drug benefits: defines "qualified prescription drug coverage," standard benefit design, and the alternative coverage standard
• 42 U.S.C. § 1395w-103 — Access to a choice of coverage: requires CMS to ensure at least two qualifying plans in every region, including a fallback PDP if competition is inadequate
• 42 U.S.C. § 1395w-104 — Beneficiary protections: mandates annual formulary disclosures, transition fill policies when formularies change mid-year, exception and appeal rights, and medication therapy management programs
• 42 U.S.C. § 1395w-111 — PDP regions and bid approval: CMS establishes geographic PDP regions, reviews actuarial bids from sponsors, and approves plans before each plan year
• 42 U.S.C. § 1395w-113 — Premiums and late enrollment penalty: sets the premium calculation formula (base beneficiary premium tracks the national average bid) and the lifetime late enrollment penalty for gaps in creditable coverage
• 42 U.S.C. § 1395w-114 — Low Income Subsidy: defines subsidy tiers, premium assistance, and reduced or eliminated cost-sharing for beneficiaries at or below 150% FPL
• 42 U.S.C. § 1395w-115 — Direct subsidy payments to plans: requires CMS to pay PDP sponsors and MA-PD plans a per-enrollee direct subsidy (historically covering about 74.5% of basic drug costs) plus reinsurance for catastrophic drug costs

How Part D Works

Plan Types

You access Part D in one of two ways. If you are in Original Medicare (Parts A and B), you enroll in a standalone Prescription Drug Plan (PDP) — a private insurer that provides drug-only coverage alongside your regular Medicare. If you are in a Medicare Advantage plan (MA-PD), your drug coverage is usually bundled into that plan; most MA plans include Part D, and you cannot generally enroll in a separate PDP while in Medicare Advantage.

Across the country, dozens of private insurers — Humana, CVS Caremark, UnitedHealth, Blue Cross, and others — compete to offer PDPs and MA-PD plans in 34 CMS-defined geographic regions. Each year, you can compare and switch plans during the Annual Enrollment Period (October 15 – December 7).

Formularies and Cost-Sharing Tiers

Every Part D plan uses a formulary — a list of covered drugs organized into tiers, typically:

• Tier 1: Preferred generics (lowest copay, often $0–$5)
• Tier 2: Non-preferred generics
• Tier 3: Preferred brand-name drugs
• Tier 4: Non-preferred brand-name drugs
• Tier 5: Specialty drugs (highest cost — often 25–33% coinsurance)

Plans must cover at minimum two drugs in every therapeutic category and class, must include all drugs in six protected classes (antidepressants, antipsychotics, anticonvulsants, immunosuppressants for organ transplants, antiretrovirals, and antineoplastics), and must provide a transition fill when formularies change.

If your drug is not on your plan's formulary or is on a non-preferred tier, you have the right to request a coverage determination and formulary exception, and to appeal if denied. Timeframes are tight — standard appeals are decided within 7 days; expedited appeals (when delay would harm health) within 72 hours.

The Out-of-Pocket Cap (Post-IRA 2022)

Before the Inflation Reduction Act of 2022, Part D had no true catastrophic cap — beneficiaries continued paying 5% coinsurance even after reaching the "catastrophic" threshold, meaning high drug users faced unlimited exposure. The ACA gradually closed the coverage gap ("donut hole") between 2010 and 2020. The IRA finished the job:

• 2024: The 5% coinsurance in the catastrophic phase was eliminated
• 2025 and after: A hard $2,000 annual out-of-pocket cap applies — once you hit $2,000 in true out-of-pocket costs (TrOOP), your plan covers 100% for the rest of the year
• Monthly payment option: Rather than hitting $2,000 in one or two months from a high-cost drug, you can opt into the Medicare Prescription Payment Plan and pay up to ~$167/month, smoothing cash flow

This cap is transformative for cancer patients, transplant recipients, and others on specialty drugs that previously cost thousands per month.

Low Income Subsidy (LIS / Extra Help)

The Low Income Subsidy — also called Extra Help — is the most underutilized benefit in Medicare. It essentially eliminates Part D premiums and cost-sharing for lower-income beneficiaries. As of 2024, the income threshold was expanded to 150% FPL (from 135% for full subsidy):

• Full LIS (below 150% FPL): $0 premium for the benchmark plan, $0 or very low copays ($4.50 generics / $11.20 brand-name in 2026 est.), no coverage gap, no late enrollment penalty
• Partial LIS (150–185% FPL, based on resources): Sliding premium subsidies and reduced cost-sharing

About 13 million beneficiaries qualify for LIS. Social Security automatically enrolls dual-eligible individuals (on both Medicare and Medicaid). Others must apply through Social Security (ssa.gov) or their State Health Insurance Assistance Program (SHIP).

Medicare Drug Price Negotiation

The Inflation Reduction Act of 2022 added a landmark new authority at 42 U.S.C. § 1395w-111(i): CMS can now negotiate prices directly with drug manufacturers for high-cost, single-source drugs with no generic competition. The first 10 negotiated drugs have prices effective January 1, 2026. This program — the "Selected Drug Subsidy Program" at § 1395w-114d — is expected to significantly reduce costs for drugs like Eliquis, Xarelto, and Januvia over the coming years, with more drugs added annually.

Manufacturers who refuse to negotiate face an excise tax of up to 95% of U.S. sales — a provision designed to make negotiation the only rational choice.

Enrollment Rules

• Initial Enrollment Period (IEP): 7 months around your 65th birthday (3 months before, month of, 3 months after)
• Late enrollment penalty: If you go 63 or more days without Part D or other creditable drug coverage after becoming eligible, you owe 1% of the national base premium per uncovered month — permanently, for as long as you have Part D
• Creditable coverage: Employer drug coverage, VA coverage, TRICARE, and some other plans count as creditable, letting you delay Part D without penalty
• Special Enrollment Periods (SEPs): Available when you lose other creditable coverage, move, gain LIS, or experience other qualifying life events

How It Affects You

State Variations

Medicare is federal, but some states supplement Part D through State Pharmaceutical Assistance Programs (SPAPs) under 42 U.S.C. § 1395w-133. States like New York (EPIC), New Jersey (PAAD), Pennsylvania (PACE), and Connecticut (ConnPACE) provide additional premium or cost-sharing assistance on top of federal benefits. SPAP benefits "wrap around" Part D — they don't displace it.

Medicaid-Medicare dual-eligible beneficiaries (over 12 million people) receive Part D through Dual Eligible Special Needs Plans (D-SNPs) or standard PDPs, with Medicaid picking up most remaining cost-sharing.

Implementing Regulations

CMS regulations implementing Part D live at 42 CFR Part 423 — Voluntary Medicare Prescription Drug Benefit (316 sections). The regulation governs every aspect of the program from plan sponsor eligibility through beneficiary appeals. Key subparts:

• § 423.30 — Eligibility: Medicare Part A or Part B enrollment required; creditable coverage rules preventing late-enrollment penalties if beneficiary had equivalent coverage elsewhere
• § 423.38 — Enrollment periods: initial enrollment (7 months around Part B eligibility), annual open enrollment (Oct 15–Dec 7), special enrollment periods for loss of other coverage
• § 423.100 — Benefit structures: standard benefit (actuarial equivalent), enhanced alternative, basic alternative; formulary requirement covering at least two drugs per therapeutic category
• § 423.120 — Access to covered drugs: adequate pharmacy network requirements; any willing pharmacy for preferred network inclusion; out-of-network access when medically necessary
• § 423.153 — Drug utilization management: prior authorization, quantity limits, step therapy programs; formulary exceptions and appeals process; medication therapy management for high-cost beneficiaries
• § 423.182 — Low-income subsidy (Extra Help): full and partial subsidy tiers; income/asset tests; automatic enrollment for dual eligibles and SSI recipients; benchmark plan premium rules
• § 423.304 — Payment to Part D sponsors: monthly payment = (risk-adjusted direct subsidy) + reinsurance subsidy + low-income cost-sharing subsidy; risk corridors; risk adjustment using prescription drug hierarchical condition categories (RxHCC model)
• § 423.505 — Contract requirements: plan sponsors must be licensed as risk-bearing entities; service area approval; disclosure requirements; CMS audit rights; intermediate sanctions
• § 423.558 — Application procedures: PDP region selection; formulary approval; actuarial attestation; marketing material review

Subpart M — Grievances, Coverage Determinations, and Appeals (§§ 423.560–423.638) sets the dispute-resolution process. A beneficiary who is denied a drug has the right to: (1) a coverage determination from the plan (72-hour standard, 24-hour expedited), (2) redetermination by the plan (7 days standard, 72 hours expedited), (3) reconsideration by an independent review entity, (4) an ALJ hearing if the amount in controversy exceeds $180, and (5) review by the Medicare Appeals Council and federal district court.

Subpart U — ALJ Hearings and MAC Review (56 sections) governs the formal administrative appeals process before the Office of Medicare Hearings and Appeals (OMHA): filing requirements, hearing procedures, evidentiary standards, and MAC review standards. Subpart T — Civil Money Penalties (48 sections) covers enforcement against plan sponsors for marketing violations, formulary discrimination, and other compliance failures — penalties up to $25,000 per beneficiary harmed.

Recent rulemakings: The IRA Part D Redesign Rule (2023) implemented the Inflation Reduction Act's restructuring of the benefit — eliminating the coverage gap ("donut hole"), establishing the $2,000 annual out-of-pocket cap (effective 2025), creating the Medicare Prescription Payment Plan for monthly cost spreading, and revising manufacturer discount obligations under the redesigned catastrophic coverage phase.

Pending Legislation

Pharmaceutical industry litigation challenges to the IRA drug price negotiation program has worked through the federal courts; most legal challenges have been rejected through 2025. The negotiated prices for the first tranche of drugs remain in effect. Future tranches will expand to biologics and additional small-molecule drugs as the program ramps up.

Recent Developments

• January 2025: $2,000 out-of-pocket cap took effect, capping unlimited catastrophic exposure for the first time in Part D's history
• January 2026: First 10 negotiated drug prices effective, including major blood thinners and diabetes drugs
• 2024 LIS expansion: Full subsidy threshold raised from 135% to 150% FPL, automatically enrolling more low-income beneficiaries in full Extra Help
• Insulin price cap: Insulin copays capped at $35/month for Part D enrollees (IRA 2022) — already saving money for the ~3.3 million Medicare beneficiaries using insulin