WASHINGTON — Consumers who use expensive brand-name prescription drugs when cheaper alternatives are available could face higher costs under a new policy being proposed by the Trump administration.

The proposal, to be published this week in the Federal Register, would apply to health insurance plans sold under the Affordable Care Act.

Health plans have annual limits on consumers’ out-of-pocket costs. Under the proposal, insurers would not have to count the full amount of a consumer’s co-payment for a brand-name drug toward the annual limit on cost-sharing. Insurers would have to count only the smaller amount that would be charged for a generic version of the drug.

For example, if a consumer filled a doctor’s prescription for a brand-name drug with a $25 co-payment, rather than using a generic medicine with a $5 co-payment, the consumer might get credit for only $5 in out-of-pocket spending. Consumers would have to spend more of their own money before reaching the annual limit on out-of-pocket costs.