Access to powerful new cholesterol-lowering drugs is so tightly controlled and patients’ out-of-pocket costs are so high that fewer than a third of people whose doctors prescribe the drugs get them, a new study found.

While highly effective, the new drugs cost as much as $14,000 annually, leading some insurers and pharmacy benefit managers to require doctors to get preapproval for them.

For example, only 47.2 percent of people who were prescribed the drugs, Praluent and Repatha, received that insurance green light, and just under two-thirds of those patients filled their prescriptions.

In the end, only 30.9 percent of people who were prescribed the drugs received them, researchers found.

These injectable drugs, called PCSK9 inhibitors, dramatically reduce levels of “bad” LDL cholesterol in the bloodstream by blocking PCSK9, a protein that is involved in how cholesterol is processed in the liver.

They are aimed at people whose LDL cholesterol levels remain high even when they take the maximum dose of regular statin drugs as well as those who have familial high cholesterol.

Even with preapproval, patient copayments ranging from $0 to $2,822 per month discouraged many from filling their prescriptions, the study found.

Whether or not a patient picked up the prescription was driven almost entirely by the out-of-pocket cost, said Dr. Ann Marie Navar, a clinical cardiologist and researcher at Duke Clinical Research Institute who was the study’s lead author.

Compared with patients who had no copayment, people who had to pay $10 were 19 percent less likely to fill their prescription. People with a $100 copay were 84 percent less likely to do so, the study found.

The study, published online in JAMA Cardiology this week, analyzed pharmacy claims data for 45,029 patients who received a new PCSK9i prescription between August 2015 and July 2016. It was funded by Amgen, which makes Repatha.

Patients who have a hard time affording the cost of these drugs should investigate the drug companies’ copay-assistance programs, as 38 percent of patients in the study did, Navar said. However, those programs aren’t typically available to patients who are covered by public programs like Medicare and Medicaid.

Beyond that, Navar’s best advice for patients is to be persistent. “Most prescriptions are rejected on the first submission and not all of those are appealed,” she said.

Updated, 5:22 p.m., to correct the description of how PCSK9 inhibitors work.

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KHN’s coverage of prescription drug development, costs and pricing is supported in part by the Laura and John Arnold Foundation.