TOPLINE

In 2026, Medicare Part D plans mostly covered the originator ustekinumab drug Stelara and several biosimilars, but patients ended up paying about the same out-of-pocket costs across products and they had little incentive to use lower gross-price options.

METHODOLOGY

• Researchers conducted a cross-sectional study using formulary and pricing files of 2026 to assess Medicare Part D coverage and expected spending for originator and biosimilar ustekinumab products in the US.
• A total of 3345 Medicare Part D plans with more than 39 million enrollees were analyzed for coverage patterns of 12 ustekinumab products, including three biosimilars labeled by manufacturers owned by companies in the portfolios of insurance plans or pharmacy benefit managers. 
• Researchers estimated annual spending by assuming six fills per patient for a 90-mg/1-mL syringe, and they used the gross per-dose prices from the first quarter of 2026. 
• Measures included coverage rates across plan types; patient out-of-pocket costs; gross annual spending per patient; and the share of drug costs paid by patients, Part D plans, manufacturers, and Medicare. 

TAKEAWAY

• Most plans (82.6%) covered Stelara, with 69.2% of enrollees in these plans. The gross price of Stelara was $8980 per fill, and most plans covered two biosimilars (mean of 2.3 biosimilars). 
• Nearly all plans (99.2%) used coinsurance, and patient out-of-pocket costs were similar across products, often reaching the $2100 Part D cap. Only Starjemza had a lower beneficiary cost under the basic plan design ($1211).
• Mean gross annual spending per patient varied substantially, from $3000 for Starjemza to $168,732 for Wezlana. 
• Plans rarely covered biosimilars labeled by subsidiaries of their affiliated pharmacy benefit managers or insurers. 

IN PRACTICE

“Plans should prioritize coverage of low gross-cost biosimilars that provide beneficiaries with lower out-of-pocket costs,” the authors wrote.

SOURCE

The study was led by Grace Castle, Vanderbilt University, Nashville, Tennessee. It was published online on August 17, 2026, as a research letter in JAMA Network Open.

LIMITATIONS

Researchers lacked data on net prices, including rebates. They did not examine the patterns of originator and biosimilar use. The study focused on Medicare Part D plan coverage. 

DISCLOSURES

The study received funding from the Commonwealth Fund and Arnold Ventures. Several authors reported receiving personal fees from private companies and health-policy organizations and grants from foundations, patient-advocacy groups, and government research agencies. One author reported having part-time employment and prior consultancy with private firms; one reported serving as a senior advisor to a federal health office. Another author reported serving on a Medicare payment advisory commission. Detailed disclosures are available in the original article.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.