In the United States, copayment or copay is a payment defined in the insurance policy and paid by the insured person each time a medical service is accessed. It is technically a form of coinsurance, but is defined differently in health insurance where a coinsurance is a percentage payment after the deductible up to a certain limit.

copayment
copayment
Drug Copayment and Adherence in Chronic Heart Failure: Effect on Cost and Outcomes
Who bears the burden of Medicaid drug copayment policies?
The differential impact of copayment on drug use in a Medicaid population.
Effect of a copayment on use of the emergency department in a health maintenance organization
Effect of a Copayment on Use of the Emergency Department in a Health Maintenance Organization — NEJM
Copayment level and compliance with antihypertensive medication: analysis and policy implications for managed care.
Impact of a prescription copayment increase on lipid-lowering medication adherence in veterans
The effect of a Medicaid drug copayment program on the utilization and cost of prescription services.