What Medicare Part D spends on generics, drug by drug

Medicare's drug benefit paid for 73.3 million prescriptions of atorvastatin in 2024, more than for any other drug, according to the Medicare Part D Spending by Drug file¹ CMS published in June 2026. The cholesterol drug reached 17.8 million enrollees. Gross spending on it came to $756 million, or $10.31 a claim, down from $14.61 a claim in 2023.

That per-claim drop was not unusual. All 20 of the most-filled drugs listed under their generic names showed lower average spending per tablet or capsule in 2024 than in 2023, by 16 to 40 percent. Across the whole program, spending on generics fell by $6.3 billion even as generic claims rose 6 percent, CMS's Part D grand totals⁴ show.

Generics are most of what Part D dispenses and a small part of what it spends. In 2024 they were 84.5 percent of claims and 11.6 percent of gross cost. The drug-level file shows which generics carry that volume, where generic dollars concentrate, and how a 2024 change in the way pharmacy fees are recorded pulled the per-claim figures down.

Where the numbers come from

CMS builds both datasets from prescription drug event records, the summaries plans submit for every Part D fill. Spending is gross drug cost, which "includes ingredient cost, dispensing fees, sales tax, and applicable vaccine administration fees" and counts what both the plan and the enrollee paid, according to the Spending by Drug methodology². It "does not reflect any manufacturers' rebates or other price concessions," which CMS is barred from disclosing. Over-the-counter drugs are excluded, as are drugs with fewer than 11 claims. Part D enrollees make up about 81 percent of Medicare beneficiaries, the methodology says.

For the brand-or-generic split in the first table, GxRadar used the grand totals CMS publishes with its Part D Prescribers data⁵. The drug-level file does not carry a generic flag. Its data dictionary³ says the brand-name field holds trademarked names for brand drugs and the plain generic name for drugs without one. GxRadar treated rows where the two names match as generics, and used only the file's "Overall" rows, which total each drug across makers. That captures 736 drug names, 1.27 billion claims and $27.8 billion in spending. It misses generics listed under shortened or formulation names, such as extended-release metformin, so it understates the generic total. We use it to rank drugs, not to measure the program.

The most-filled generics

Statins, blood pressure drugs, thyroid hormone and acid reducers fill the top of the list. Twelve generics each topped 23 million claims in 2024, according to the 2024 file¹. Spending per claim is not the cost of a standard fill, because a Part D claim can be a 30-day or 90-day supply and the figures include dispensing fees. GxRadar's NADAC price pages track what pharmacies pay to buy each drug.

CMS's manufacturer column is a count of companies with claims under each drug name, from 15 for omeprazole to 40 for gabapentin. The 20 most-filled generics accounted for 46 percent of the claims in GxRadar's generic subset.

Where the generic dollars go

Volume and spending part ways quickly. The largest generic line by spending was lenalidomide, a cancer drug, at $2.64 billion on 198,067 claims, or about $13,300 a claim. That one drug outspent atorvastatin by more than three to one. Abiraterone, a prostate cancer drug, was third at $693 million. The 10 highest-spending generic names took 25 percent of spending in the subset, and the top 50 took 52 percent.

Who pays differs by drug type as well. Plans bore 49 percent of the $36.1 billion in gross generic spending in 2024, the Medicare Payment Advisory Commission reported in its July 2026 data book⁷, using its own brand and generic classification. Medicare's reinsurance covered 15 percent, the low-income subsidy 18 percent and enrollees' cost sharing 19 percent. For brand-name drugs, enrollee cost sharing was 5 percent of gross spending. MedPAC put the overall generic dispensing rate at 90 percent of prescriptions standardized to a 30-day supply. GxRadar's earlier piece on the generic share of Part D tracks the grand totals back to 2013.

Why 2024 spending fell

From 2023 to 2024, generic gross cost fell 15.8 percent while generic claims rose 6.2 percent. Generic cost per claim dropped from $29.25 to $23.19.

That drop lines up with a rule CMS finalized in May 2022. Starting Jan. 1, 2024, the final rule⁶ redefined a drug's "negotiated price" as "the lowest possible reimbursement" a network pharmacy will receive for it. Before then, plans and their pharmacy benefit managers often collected fees from pharmacies after a claim was paid, so the price recorded at the counter was higher than the amount the pharmacy finally kept. The rule moved those fees to the point of sale, and the recorded gross cost fell with them.

Generics took the largest hit. In 2023, MedPAC found, pharmacy fees equaled 12 percent of gross spending for generic drugs and 7 percent for brand-name drugs. With the rule in place, retroactive pharmacy fees fell to just under 1 percent of gross Part D spending, from 8 percent. Some of the 2024 drop therefore reflects bookkeeping rather than lower acquisition prices, and comparisons across that year need care. NADAC¹⁰, which surveys pharmacy invoice prices under a CMS methodology¹¹ that leaves out anything not on the invoice, does not include fees of this kind. The two measures diverged in 2024. Part D spending per unit of amlodipine, across all strengths, fell 27 percent, while the average NADAC for the 5 mg tablet rose 6 percent. For rosuvastatin, Part D spending per unit fell 40 percent and the 10 mg tablet's average NADAC fell 14 percent.

For more on the mechanics, GxRadar explains how Part D pays for generics and what a pharmacy benefit manager does.

What the next release will show

The 2024 file is the latest annual edition. CMS's preliminary quarterly file⁸, posted in July 2026, already carries full-year 2025 totals, though its methodology⁹ warns that the data are less mature and advises "caution when comparing between the annual and quarterly datasets." In it, atorvastatin again leads with 76.1 million claims and $818 million in gross spending, or $10.75 a claim. Lenalidomide's spending rose to $3.93 billion. The final 2025 annual file will be the first to reflect the Inflation Reduction Act¹²'s $2,000 cap on enrollees' yearly out-of-pocket costs, which rose to $2,100 in 2026, according to CMS's 2026 program instructions¹³. GxRadar's guide to Part D changes in 2025 and 2026 covers the redesign, and our 2026 plan guide covers premiums.