Laws passed by many states that require health plans to charge the same cost-sharing amounts for cancer patients receiving chemotherapy — regardless of whether they get the medication intravenously or take a pill or liquid by mouth — are providing uneven pocketbook protection, according to a new study.

These “parity” laws became popular as the number of pricey anti-cancer oral medications grew, but consumers were seeing a disparity in how insurance handled the patients’ share of the treatment.

In many plans, oral anti-cancer drugs were placed in high cost-sharing tiers in patients’ prescription coverage while the drug infusions — which took place at a doctor’s office — were handled as an office visit and generally required less out-of-pocket costs for patients, sometimes just a minimal copayment.

The study, published online in JAMA Oncology recently, analyzed the health plan claims of 63,780 adult cancer patients younger than age 65. All lived in states that passed parity laws from 2008 to 2012.

State parity laws don’t apply to “self-funded” employer health plans that pay their workers’ claims directly rather than buying state-regulated insurance policies. Just under half of the patients studied were covered by self-funded plans. Researchers compared the use of oral anti-cancer medicines and out-of-pocket spending between patients in the self-funded plans and those in state-regulated plans to determine the impact of parity laws.

The study found that the laws benefited those with lower monthly out-of-pocket spending more than those whose monthly spending for oral chemotherapy drugs was higher. According to the research, the proportion of prescriptions for oral drugs that did not require a patient’s copayment grew from 15 to 53 percent over the study period in health plans that were subject to state parity laws. That was more than double the increase in plans that were not subject to parity laws, which increased from 12.3 to 18 percent.

The finding surprised researchers, said Stacie Dusetzina, an assistant professor of pharmacy and public health at the University of North Carolina-Chapel Hill, who was the study’s lead author.

At the other end of the spectrum, the number of prescriptions requiring high out-of-pocket spending grew, despite parity laws. The proportion of prescriptions filled in plans subject to parity that cost more than $100 out-of-pocket per month increased from 8.4 to 11.1 percent, the study found. That figure declined slightly for prescriptions in plans that weren’t subject to parity, from 12 to 11.7 percent.

“We are a bit concerned about that finding, because when you think about who would have been the target of the law, parity is intended to help people afford the cost of their treatment,” Dusetzina said. “The most expensive fills got more expensive after parity. That’s concerning.”

The researchers suggested that continuing growth in high-deductible plans and high coinsurance charges may have contributed to the rise in the number of patients with high out-of-pocket costs for cancer treatment, even in states that have parity laws.

The study also found that out-of-pocket spending on infused drugs, which are typically older and less expensive than oral anti-cancer therapies, remained stable during the study period and was unaffected by parity laws.

A federal law that would extend parity to the seven states that don’t have it has been proposed in the past, most recently in March. Such a law could also benefit people in self-funded plans that aren’t subject to state laws, as well as Medicare beneficiaries.

“A federal law would potentially provide a lot of benefit, because we do feel parity has a net benefit for patients,” Dusetzina said.