Traditionally, the idea of insurance was to spread the costs of paying for the sick.

“This is an erosion of the traditional concept of insurance,” Mr. Mendelson said. “Those beneficiaries who bear the burden of illness are also bearing the burden of cost.”

And often, patients say, they had no idea that they would be faced with such a situation.

It happened to Robin Steinwand, 53, who has multiple sclerosis.

In January, shortly after Ms. Steinwand renewed her insurance policy with Kaiser Permanente, she went to refill her prescription for Copaxone. She had been insured with Kaiser for 17 years through her husband, a federal employee, and had had no complaints about the coverage.

She had been taking Copaxone since multiple sclerosis was diagnosed in 2000, buying a 30 days’ supply at a time. And even though the drug costs $1,900 a month, Kaiser required only a $20 co-payment.

Not this time. When Ms. Steinwand went to pick up her prescription at a pharmacy near her home in Silver Spring, Md., the pharmacist handed her a bill for $325.

There must be a mistake, Ms. Steinwand said. So the pharmacist checked with her supervisor. The new price was correct. Kaiser’s policy had changed. Now Kaiser was charging 25 percent of the cost of the drug up to a maximum of $325 per prescription. Her annual cost would be $3,900 and unless her insurance changed or the drug dropped in price, it would go on for the rest of her life.

“I charged it, then got into my car and burst into tears,” Ms. Steinwand said.

She needed the drug, she said, because it can slow the course of her disease. And she knew she would just have to pay for it, but it would not be easy.