Nobody likes paying a lot for health insurance, but at least it provides peace of mind. Even while we grumble about steadily rising deductibles and co-pays, we figure if we get really sick — with cancer, say — then insurance will handle the bills.

It’s not a safe assumption. A growing number of cancer patients are being stuck with exorbitant bills for chemotherapy drugs because of a common insurance policy loophole.

Basically, insurance companies often cover just a fraction of the cost of a needed cancer medication if it’s taken in the form of pills. The companies reimburse the full price only if the patient receives the drug intravenously.

That’s a problem because many new cancer drugs are supposed to be taken orally or are available only in pill form. In some cases, the same drug is covered by insurance if taken via injection and not covered if it’s taken orally. The difference in out-of-pocket cost to the patient can run in the thousands of dollars a month.

Cancer doctors, hospitals and patient advocacy groups decry the discrepancy as outrageous. There’s a nationwide campaign to eliminate it, including a bill in Congress. The District of Columbia and 13 states have passed laws in the past three years to require parity between oral and intravenous chemotherapy drugs. The discrepancy has been fixed for Medicare.

But some insurance companies and budget-conscious legislators are resisting change. The disparity still exists in Virginia and Maryland, and it’s uncertain whether those states will eliminate the problem any time soon.

“It’s a dollar issue,” said Paul Celano, president of the Maryland Society of Clinical Oncology. “Everyone agrees in principle that patients should be able to get their cancer care, and there shouldn’t be this insurance dodge that they’re charged a substantially different rate because of the type of medication.”

In Virginia, a parity bill was introduced in the General Assembly session but died in committee. A Maryland bill was withdrawn because of concerns it would cost the state millions of dollars to reform coverage for state employees.

One victim of Maryland’s failure to act is Kate S., a 51-year-old mother of three who lives in Anne Arundel County. Since August, she has received diagnoses of unrelated cancers of the brain and breast. She spoke on the condition that I not publish her surname, for privacy’s sake.

After Kate had surgery to remove the brain tumor, her doctors at Johns Hopkins Hospital in Baltimore put her on six weeks of daily doses of two pills of the chemotherapy drug Temodar.

The medication cost $10,800. Her insurance company paid $2,000. Kate said her provider told that if she’d taken the identical drug intravenously, she wouldn’t have paid a dime.

“I was really shocked by this, and they told me it was very common,” Kate said. She didn’t learn about the discrepancy until two weeks into the treatment.

“It wasn’t presented to me as an option to do it intravenously. They told me, this is what you do,” Kate said.

Soon she’ll begin a second round of chemotherapy, for six months. She estimates that will cost her $15,000 unless she opts for intravenous treatment. Her doctors recommend against that, and it would be less pleasant and convenient. She’d have to go regularly to a clinic to spend hours sitting with a needle in her arm, rather than swallowing pills at home.

Kate said that the cost is a burden but that she has savings to cover it. It would be severe for others with less money, she said.

“This is a rough time for a lot of people. They may have to make a decision to go in for [intravenous] infusions just because they don’t want to go into debt,” Kate said.

That’s just the kind of person that led state Sen. Jamie B. Raskin, D, to co-sponsor a parity bill in Annapolis.

A colon cancer survivor, Raskin heard complaints about the oral-intravenous discrepancy while receiving chemotherapy in clinics.

“Sitting in the rooms where chemo is administered, I met people who would have preferred to be using the pill form but whose insurance plans weren’t covering it,” Raskin said. He plans to resubmit a bill in the session beginning in January.

Cancer patients have enough worries without anxiety over whether they can afford the drug recommended by their doctor. Because any of us is vulnerable to the disease, parity would add peace of mind for everyone.

Robert McCartney is a Washington Post columnist.