More than 1 million people in the Medicare drug program next year will pay almost the full price for certain brand-name drugs when they choose them over generics — a move that advocates for patients say is not clearly spelled out by the government nor insurers.

For hundreds of targeted drugs, patients will pay a standard co-payment. They also will pay the difference in price between the brand- name medicine and the generic. The practice in Medicare mirrors similar efforts in job-based insurance.

Medicare says about 10% of insurers will use the extra charge next year.