SAN FRANCISCO (KGO) -- There's a new trend in health insurance to pass along the costs of the highest price medications to patients. Instead of a co-pay, patients are finding expensive drugs for cancer, arthritis and multiple sclerosis can cost them hundreds, even thousands of dollars out of pocket each month, but a Bay Area lawmaker is working to change that.

"My neurologist said, 'You need to let your insurance company know that every day that goes by that you don't take this drug, they are costing you neurological function,'" said MS patient Melanie Rowen.

That drug Rowen needed to manage her MS cost her nearly $700 a month. Her insurance classified it as a specialty tier drug, also known as Tier 4. That means she pays 30 percent of the cost of the drug rather than a simple co-pay.

When asked how she made it work financially, Rowen said, "I went into credit card debt."

"What we're hearing is things such as, 'What do I do? Do I pay my mortgage?' or 'Do I go into debt?' which is a common thing, people are going into debt or they're going without some of the essentials of life," said Stewart Ferry, the public policy director for the National MS Society.

Of the 12 most common Tier 4 drugs, four are used to treat MS.

"They're just so frustrated because they're paying their premiums and this runs completely counter to what insurance is supposed to be about, which is equitably spreading the risk. So this is antithetical to the very nature of insurance," said Ferry.

Specialty tier pricing started under Medicare Part D. Michelle Vogel is executive director of the Alliance for Plasma Therapies and has been tracking the impact.

"Whatever happens with Medicare typically follows in private insurance, so when I was looking at the private plans, and especially in California, you're seeing the majority of plans have put in Tier 4 plans," said Vogel.

There's a wide range of illnesses and diseases impacted by this change: cancer, rheumatoid arthritis, even hemophilia and organ transplantation.

"If you get a transplant, but the anti-rejection drug is too expensive to pay for, then why bother transplanting to begin with? You'll die without that organ," said Vogel.

"Sixty-one percent of Americans take some sort of prescription medication a day. So it is alarming when health plans are reclassifying drugs into a new Tier 4 category," said Assm. Fiona Ma, D-San Francisco.

Ma is proposing legislation in California to prevent health insurers from moving vital medications to Tier 4 status.

"What we're trying to do is make sure that patients are able to afford the medication they need. So we are going to look at a cap system as well as cost containment for the individuals who are on medication," said Ma.

"What the cost is of a given drug starts with the manufacturer. We ought to look there and then both the health plan and the individual have roles to play in contributing to the cost of the drug," said Patrick Johnston, CEO of the California Association of Health Plans.

Johnston is concerned about legislation that prevents cost sharing.

"If we have a drug co-pay that is tiered, then we can control the cost and make it more likely that more people can afford insurance," said Johnston.

But a growing number of patients like Rowen are finding themselves facing a huge financial burden simply to get the drugs their doctors have prescribed.

"The stakes are high and nobody who has any choice about it is going to choose not to take them. It's absolutely out of the question," said Rowen.

Right now, New York is the only state with a law preventing specialty tiers. Ma plans to announce the specifics of her legislation on Thursday. However, state legislation does not impact self-funded health plans which cover about half of all employees with health insurance. Federal legislation is needed to change that.