Health Outcome Changes in Individuals With Type 1 Diabetes After a State-Level Insulin Copayment Cap

Importance Many insulin users ration doses due to high out-of-pocket costs. Starting January 2020 with Colorado, 25 states and the District of Columbia enacted laws that cap insulin copayments. Objective To estimate the association of Colorado’s 100 copayment cap with out-of-pocket spending, medication adherence, and health care services utilization for diabetes-related complications. Design, Setting, and Participants In this cohort study using Colorado’s All-Payer Claims Database, nonelderly insulin users with type 1 diabetes were analyzed from January 2019 to December 2020. Outcome changes were compared in the prepolicy and postpolicy period among individuals continuously enrolled in state-regulated and non–state-regulated plans using difference-in-differences regressions. Subgroup analyses were conducted based on individuals’ prepolicy spending (low: never ≥100 out-of-pocket vs high: ≥100 out-of-pocket cost at least once). Data were analyzed from June 2023 to May 2024. Exposure Enrollment in state-regulated health insurance plans subject to the copayment cap legislation. Main Outcomes and Measures Adherence to basal and bolus insulin treatment was evaluated using the proportion of days covered measure, out-of-pocket spending reflected prescription cost for a 30-day supply, and health care utilization for diabetes-related complications was identified using primary diagnosis codes from medical claims data. Results The panel included 1629 individuals with type 1 diabetes (39 096 person-months), of which 924 were male (56. 7%), 540 (33. 1%) had 1 or more comorbidities, and the mean (SD) age was 40. 6 (15. 9) years. Overall, the copayment cap was associated with out-of-pocket spending declines of 17. 3 (95% CI, −27. 3 to −7. 3) for basal and 11. 5 (95% CI, −24. 7 to 1. 7) for bolus insulins and increases in adherence of 3. 2 (95% CI, 0. 0 to 6. 5) percentage points for basal and 3. 3 (95% CI, 0. 3 to 6. 4) percentage points for bolus insulins. Changes in adherence were associated with increases within the prepolicy high-spending group (basal, 9. 9; 95% CI, 2. 4 to 17. 4 percentage points; bolus, 13. 0; 95% CI, 5. 1 to 20. 9 percentage points). The policy was also associated with a mean reduction of −0. 09 (95% CI, −0. 16 to −0. 02) medical claims for diabetes-related complications per person per month among high spenders, a 30% decrease. Conclusions and Relevance In this cohort study of Colorado’s insulin copayment cap among individuals with type 1 diabetes, the policy was associated with an overall decline in out-of-pocket spending, an increase in medication adherence, and a decline in claims for diabetes-related complications only among insulin users who spent more than 100 in the prepolicy period at least once.