Cost-Sharing Caps Boost Insulin Refills for Medicare Part D Enrollees

The Inflation Reduction Act’s limit on out-of-pocket insulin costs is associated with more Medicare Part D enrollees getting their insulin prescriptions filled, according to a new analysis published in JAMA. More of these people paid $35 or less for their insulin prescriptions compared with people aged 60 to 64 without Medicare Part D plans.

The number of Medicare Part D enrollees taking insulin doubled, but out-of-pocket spending on insulin quadrupled from 2007 to 2020. In 2007, Medicare Part D patients spent $236 million on insulin, a figure that surpassed $1 billion in 2020, according to KFF research published last year.

Since January 2023, the Inflation Reduction Act (IRA) has capped cost-sharing for a one-month supply of insulin at $35 for all Part D beneficiaries. A group of researchers from the University of Wisconsin and the University of Southern California (USC) sought to understand the impact of this legislation on insulin usage and adherence.

John A. Romley, Ph.D.

“The number of monthly insulin fills with Medicare Part D increased by about 50,000 due to the Inflation Reduction Act," John A. Romley, Ph.D., coauthor of this study and assistant professor at the School of Public Policy and the School of Pharmacy at USC, told Formulary Watch in an interview.

The researchers analyzed data on about 14 million insulin prescription fills from September 2021 through April 2023 using IQVIA’s National Prescription Audit. They focused on two groups. The first group included people aged 65 to 74 enrolled in Medicare Part D with the $35 insulin price cap. The second group included people aged 60 to 64 who were not yet enrolled in Medicare and did not have the $35 price cap. To compare insulin use in these groups, the researchers analyzed pharmacy fill data from September 2021 through December 2022 and from January 2023 through April 2023 — before and after the IRA’s insulin cap on cost-sharing went into effect.

The results showed that the number of insulin fills for people with Medicare increased from 519,588 per month in the pre-IRA period to 523,564 per month after the law went into effect. In contrast, the number of insulin fills among people without Medicare decreased from 344,719 per month to 330,229 per month. In addition, the average number of monthly fills with cost sharing of $35 or less increased from 340,509 in the pre-IRA period to 366,928 after the IRA provisions became effective.

“Of the 50,000 new monthly fills of insulin observed in Medicare, about 20,000 of those represent individuals previously unable to afford insulin," Romley said. "For those 20,000, initiating insulin reduces the rate of serious complications from diabetes, such as amputations, vision loss, and heart attacks."

He continued, “Of course, these complications are terrible for patients and their families, but are also quite costly for the healthcare system as a whole."

Romley explained that healthcare payers outside of Medicare need better incentives to offer similar price caps on insulin. “One of the challenges here is that some of the benefits of accessing and using drugs [like insulin] come in the long term,” he said. “Consider a 60-year-old who has commercial insurance. The plan administrators, when deciding how to structure the costs and copays, are not going to see those benefits necessarily. Some of those may come later after the person ages out of commercial insurance and goes on Medicare. And so there's an incentive problem there that I think we should be thinking about.”