A new analysis led by researchers at the Johns Hopkins Bloomberg School of Public Health finds that insulin copay caps for Medicare Part D beneficiaries keep insulin prices in check.
The Inflation Control Act of 2022 mandated a $35 out-of-pocket cap for a 30-day supply of insulin for Medicare Part D beneficiaries starting January 1, 2023. This is the first time the federal government has imposed a cap on insulin prices for all Medicare beneficiaries.
For the study, researchers analyzed Medicare claims data for approximately 3.8 million patients who claimed insulin at least once during a five-year period from 2019 to 2023.
The proportion of these patients who paid $35 or less out-of-pocket for a 30-day supply increased from 48% in 2019 to 75% in 2023.
The findings were published online March 19 in a peer-reviewed research letter. Japan Automobile Manufacturers Association.
The study also showed that the average out-of-pocket cost for that amount of insulin fell from $50.87 in 2019 to $21.98 in 2023. Cost declines from 2019 to 2023 were seen in every U.S. state. This study is believed to be the first to analyze the effects of inflation control methods on insulin caps.
“This is compelling evidence that recent Medicare policies have achieved their intended purpose of improving insulin access and affordability,” said study lead author Michael Huang, Ph.D., MHS, assistant professor in the Bloomberg School’s Department of Epidemiology. “Insulin costs for Medicare enrollees are currently at historically low levels.”
The researchers noted that the finding that about a quarter of Medicare beneficiaries paid more than $35 for 30 days of insulin in 2023 was unexpected. Their analysis found that these beneficiaries had at least one prescription that did not prorate up to the Inflation Control Act limits.
Approximately 3.8 million Medicare beneficiaries use insulin as a treatment for type 1 or type 2 diabetes. Insulin is used to replace the natural metabolic hormone of the same name, but its production is virtually absent in type 1 diabetes, and its production is also impaired in many cases of type 2 diabetes.
To help beneficiaries contain their insulin costs, the Centers for Medicare and Medicaid Services (CMS) has capped out-of-pocket costs for 30 days at $35 in 2021 in a limited, voluntary initiative. The Inflation Control Act of 2022 mandates a 30-day out-of-pocket maximum of $35 for Medicare Part D beneficiaries, effective January 1, 2023.
The study included all Medicare Part D patients who had at least one claim for insulin during the study period and did not receive Medicare low-income subsidies. The researchers grouped the claims data into five calendar years, from 2019 to 2023, for their analysis.
Regarding Medicare Part D beneficiaries using insulin still paying more than $35 for a 30-day supply in 2023, Fang points out that CMS’s official guidance only applies the $35 rule to multiples of 30 days. “If the prescription is somewhere in between, the patient can be billed up to a multiple of the next month,” Huang says. “For example, your health insurance policy may treat a 45-day supply as the same as a 60-day supply and charge you up to $70.”
He added that the variation in average 30-day insulin costs by state (from $10.36 in Washington, D.C., to $31.09 in Minnesota in 2023) may partially reflect state-level differences in how Medicare insurance plans handle pro-rata calculations.
Researchers are currently investigating the issue of prorating prescriptions outside the current 60-day and 90-day supply windows, looking more closely at how average costs vary across plans and whether policy changes are needed to close the gap.
“Trends in insulin copayments among U.S. Medicare beneficiaries” was co-authored by Michael Fang, Chen Dun, Dan Wang, Caitlin Hicks, Elizabeth Selvin, Jung-Im Shin, and Mariana Socal.
Research support was provided by the National Institute of Diabetes and Digestive and Kidney Diseases (K01DK138273, R01DK139324).
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Johns Hopkins University Bloomberg School of Public Health
Reference magazines:
Fang, M. Others. (2026). Trends in insulin copayments among U.S. Medicare beneficiaries. Japan Automobile Manufacturers Association. https://doi.org/10.1001/jama.2026.2341. https://jamanetwork.com/journals/jama/article-abstract/2846650
