EFFECTS OF INSULIN COPAYMENT CAPS AND COINSURANCE ON USE, ADHERENCE, AND OUT-OF-POCKET SPENDING IN THE UNITED STATES: A SYSTEMATIC REVIEW
Author(s)
Caleb Ochimana, BPharm, MBA, MPH1, Huiwen Zheng, Msc2, Esmeralda Rodgers, MLIS, AHIP3, Robert L. Ohsfeldt, PhD4, Ukert Benjamin, PhD4, Alva Ferdinand, DrPH, JD2, Jason E. Maddock, Ph.D.5;
1Texas A&M School of Public Health, Health Policy and Management, College Station, TX, USA, 2Texas A&M University School of Public Health, Health Policy and Management, College Station, TX, USA, 3Texas A&M University, Medical Sciences Library, Round Rock, TX, USA, 4Texas A&M University, Health Policy and Management, College Station, TX, USA, 5Texas A&M University, Environmental and Occupational Health, College Station, TX, USA
1Texas A&M School of Public Health, Health Policy and Management, College Station, TX, USA, 2Texas A&M University School of Public Health, Health Policy and Management, College Station, TX, USA, 3Texas A&M University, Medical Sciences Library, Round Rock, TX, USA, 4Texas A&M University, Health Policy and Management, College Station, TX, USA, 5Texas A&M University, Environmental and Occupational Health, College Station, TX, USA
OBJECTIVES: To systematically review recent U.S. evidence on the effects of insulin copayment caps and coinsurance levels on insulin use, medication adherence, out-of-pocket (OOP) spending, and healthcare utilization among adults with diabetes.
METHODS: We conducted a systematic review following PRISMA 2020 guidelines. MEDLINE, Embase, Web of Science, and the Cochrane Library were searched for studies published between January 2020 and November 2025. Eligible studies included observational and quasi-experimental designs, such as difference-in-differences and pre-post analyses with comparison groups, that evaluated insulin cost-sharing policies. Two reviewers independently screened studies, extracted data using standardized templates, and assessed risk of bias using ROBINS-I. Findings were synthesized narratively following SWiM guidance and stratified by outcome domain, insurance type, and policy context.
RESULTS: Fourteen studies met inclusion criteria from 1,981 identified records. Most studies employed quasi-experimental designs and large administrative claims or nationally representative survey data, with sample sizes ranging from tens of thousands of beneficiaries to national populations of insulin users. Twelve studies (86%) reported statistically significant reductions in insulin-related OOP spending following implementation of copayment caps or reduced coinsurance, with several studies documenting relative reductions exceeding 20%. Nine studies (64%) reported increases in insulin prescription fills, days’ supply, or adherence measures such as proportion of days covered, with improvements most consistently observed among Medicare beneficiaries and commercially insured populations subject to state or federal caps. Evidence on healthcare utilization was mixed: five studies reported reductions in diabetes-related hospitalizations or emergency department visits, while others found no significant short-term changes. Overall risk of bias was assessed as low to moderate, with stronger internal validity among quasi-experimental studies.
CONCLUSIONS: Insulin cost-sharing reductions are consistently associated with lower patient OOP spending and modest but meaningful improvements in insulin use and adherence, while short-term effects on healthcare utilization remain heterogeneous.
METHODS: We conducted a systematic review following PRISMA 2020 guidelines. MEDLINE, Embase, Web of Science, and the Cochrane Library were searched for studies published between January 2020 and November 2025. Eligible studies included observational and quasi-experimental designs, such as difference-in-differences and pre-post analyses with comparison groups, that evaluated insulin cost-sharing policies. Two reviewers independently screened studies, extracted data using standardized templates, and assessed risk of bias using ROBINS-I. Findings were synthesized narratively following SWiM guidance and stratified by outcome domain, insurance type, and policy context.
RESULTS: Fourteen studies met inclusion criteria from 1,981 identified records. Most studies employed quasi-experimental designs and large administrative claims or nationally representative survey data, with sample sizes ranging from tens of thousands of beneficiaries to national populations of insulin users. Twelve studies (86%) reported statistically significant reductions in insulin-related OOP spending following implementation of copayment caps or reduced coinsurance, with several studies documenting relative reductions exceeding 20%. Nine studies (64%) reported increases in insulin prescription fills, days’ supply, or adherence measures such as proportion of days covered, with improvements most consistently observed among Medicare beneficiaries and commercially insured populations subject to state or federal caps. Evidence on healthcare utilization was mixed: five studies reported reductions in diabetes-related hospitalizations or emergency department visits, while others found no significant short-term changes. Overall risk of bias was assessed as low to moderate, with stronger internal validity among quasi-experimental studies.
CONCLUSIONS: Insulin cost-sharing reductions are consistently associated with lower patient OOP spending and modest but meaningful improvements in insulin use and adherence, while short-term effects on healthcare utilization remain heterogeneous.
Conference/Value in Health Info
2026-05, ISPOR 2026, Philadelphia, PA, USA
Value in Health, Volume 29, Issue S6
Code
P10
Topic
Health Policy & Regulatory
Topic Subcategory
Health Disparities & Equity, Insurance Systems & National Health Care, Pricing Policy & Schemes, Reimbursement & Access Policy
Disease
No Additional Disease & Conditions/Specialized Treatment Areas, SDC: Diabetes/Endocrine/Metabolic Disorders (including obesity)