What’s Driving Billions in Part B & D Spending? 10 Most Expensive Drugs in Medicare

In the ever-evolving world of healthcare, a tiny fraction of prescription drugs are swallowing up enormous chunks of Medicare’s budget. From eye injections to cancer infusions to everyday pills for heart health, just 20 drugs account for over $75 billion in combined Medicare Part B and Part D spending.

But what are these drugs? Who makes them? And why are they so expensive?

Let’s dig into the top 10 drugs for each Medicare program—Part B (injected/infused drugs administered in a clinic) and Part D (retail pharmacy prescriptions)—and explore the financial forces behind them.

💰 Part D: The Top 10 Outpatient Drugs by Spending (CY 2023)

These are the pills and insulin products seniors pick up at the pharmacy. According to CMS’s negotiated price fact sheet, these 10 drugs alone racked up $56.2 billion in 2023:

📊 Top 10 Medicare Part D Drugs by Gross Spending

(Click chart to enlarge)

← this is a reference to the chart shown earlier.

Notable takeaway: Eliquis alone made up nearly a third of the entire top-10 spending. It had no generic competition and was used by over 3.7 million beneficiaries.

💉 Part B: The Top 10 Clinic-Administered Drugs by Spending (CY 2021)

CMS hasn’t released full 2023 data for Part B yet, but the latest available stats (from 2021) tell a compelling story. The top 10 drugs accounted for nearly half of all Part B drug spending:

📊 Top 10 Medicare Part B Drugs by Total Spending

(Click chart to enlarge)

Notable takeaway: Just three oncology drugs—Keytruda, Opdivo, and Rituxan—accounted for over $6.6 billion in Part B spending.

📈 What’s Driving the Costs?

🧪 The Policy Shift: IRA, Rebates, and Negotiations

The Inflation Reduction Act (IRA) is already beginning to shift the landscape:

• Part D drug prices will be directly negotiated by CMS starting in 2026. All 10 drugs listed in the 2023 chart are up first.

• Insulin prices have been capped, and other out-of-pocket protections for seniors will roll out by 2025.

• Inflation penalties are in place—manufacturers face rebates if prices rise faster than inflation.

Meanwhile, biosimilars for big-name Part B drugs like Eylea and Keytruda are expected to launch between 2025–2027, which may gradually chip away at the brand monopolies.

🧭 What to Watch in 2025 and Beyond

1. GLP-1 Weight Loss Drugs (Ozempic, Wegovy) – Spending is already exploding. Expect them to appear in top 10s within 2 years.

2. Biosimilar market evolution – Will physicians switch? Will Medicare incentivize biosimilar use effectively?

3. Negotiation outcomes – How deep will the discounts go when the first negotiated prices take effect in 2026?

🧠 Final Thoughts

It’s clear that a tiny slice of drugs dominate Medicare drug spending, driven by strong patent protection, growing patient volumes, and limited alternatives.

But the coming years could reshape the map entirely—negotiated prices, biosimilars, and cost caps might finally bend the Medicare drug cost curve. Until then, understanding these top spenders is key to grasping what drives America’s drug bill.