Association of State Insulin Out-of-Pocket Caps With Insulin Cost-Sharing and Use Among Commercially Insured Patients With Diabetes: A Pre-Post Study With a Control Group

Background: Twenty-five states have implemented insulin out-of-pocket (OOP) cost caps, but their effectiveness is uncertain. Objective: To examine the effect of state insulin OOP caps on insulin use and OOP costs among commercially insured persons with diabetes. Design: Pre-post study with control group. Setting: Eight states implementing insulin OOP caps of $25 to $30, $50, or $100 in January 2021, and 17 control states. Participants: Commercially insured persons with diabetes and insulin users younger than 65 years. Subgroups of particular interest included members from states with insulin OOP caps of $25 to $30, enrollees with health savings accounts (HSAs) that require high insulin OOP payments, and lower-income members. Measurements: Mean monthly 30-day insulin fills and OOP costs. Results: State insulin caps were not associated with changes in insulin use in the overall population (relative change in fills per month, 1.8% [95% CI, -3.2% to 6.9%]). Insulin users in intervention states saw a 17.4% (CI, -23.9% to -10.9%) relative reduction in insulin OOP costs, largely driven by reductions among HSA enrollees; there was no difference in OOP costs among nonaccount plan members. More generous ($25 to $30) state insulin OOP caps were associated with insulin OOP cost reductions of 40.0% (CI, -62.5% to -17.6%), again primarily driven by a larger reduction in the subgroup with HSA plans. Limitations: Single national insurer; 9-month follow-up. Conclusion: Insulin OOP caps were associated with reduced insulin OOP costs but no overall increases in insulin use. A proposed national insulin cap of $35 for commercially insured persons might lead to meaningful insulin OOP savings but have a limited effect on insulin use.