Fourteen thousand three hundred nine drug-manufacturer records sit in Medicare's Part D spending data. Strip out the manufacturer-level duplicates and you're left with 3,598 distinct drugs that together cost the program $275.9 billion in the most recent reporting year. The top 10 of those 3,598 drugs — 0.3% of the list — account for $71.1 billion, or 25.8% of all Part D spending. Widen the lens to the top 15 and the share climbs to 31%. Medicare Part D spend is not a broad plain; it's a spike.
What's striking is why each drug lands on that spike, because two completely different mechanisms get you there. Eliquis (apixaban), the single largest line item at $18.3 billion, reaches the top by volume: 3.9 million beneficiaries at a relatively modest $4,652 per patient per year. Stelara (ustekinumab), by contrast, generated $3.0 billion from just 22,930 beneficiaries — $130,300 per patient. Humira, Revlimid, Xtandi, and Biktarvy follow the same specialty-drug math: tiny patient populations, five- and six-figure per-patient costs, and a spot in the top 15 anyway. Mass-market chronic-disease drugs and ultra-priced specialty drugs are converging on the same total-spend number through opposite routes — one is "priced to the market," the other "priced to the disease."
The mechanism: list price, not volume, decides who gets negotiated
This concentration is exactly what the Inflation Reduction Act's Medicare Drug Price Negotiation Program was built to target. CMS selects the highest-total-spend drugs still without generic or biosimilar competition, and the overlap with our top-15 list is direct: Eliquis, Jardiance, Xarelto, Januvia, Farxiga, Entresto, and Stelara — seven of the fifteen highest-spending drugs in this index — were among the first ten drugs CMS selected for negotiation, with negotiated prices taking effect January 1, 2026 (a minimum 38% cut off 2023 list prices)[1][2]. Eliquis's negotiated price is $231 versus a $521 list price; Stelara drops from $13,836 to $4,695[2]. Because negotiation eligibility is a function of aggregate Part D spend, the same concentration that makes this list top-heavy is what made these specific drugs regulatory targets first.
Caveats worth naming
This index reports gross drug cost — list-price-adjusted claims — and, like CMS's own public dataset, it cannot reflect manufacturer rebates, which CMS is statutorily barred from disclosing[3]. Net spending after rebates is materially lower for several of these drugs, especially insulins and PCSK9 inhibitors, so gross-cost rankings overstate true program cost for heavily rebated products. The data also reflects a single latest reporting year (2023) per drug rather than a real-time feed, and manufacturer-level and "Overall" rows coexist in the raw index, which will double-count totals if not filtered out, as we did here.
Why this matters going forward: as more negotiated prices phase in for 2027 and beyond, and as GLP-1 drugs like Ozempic ($9.2 billion, already the #2 line item) continue climbing, the list of drugs driving Part D spend is likely to keep shrinking in count even as dollar concentration holds or grows — making a small number of pricing and negotiation decisions disproportionately consequential for the whole program.