Medicare plans place few restrictions on the coverage of prescription opioids, despite federal guidelines recommending such restrictions, a new Yale study finds. The research results highlight an untapped opportunity for Medicare formularies to limit opioid prescribing, the researchers said.

The findings were published in the journal Annals of Internal Medicine.

The risk of opioid overdoses rises when individuals are prescribed opiates at high dosages. While the Centers for Disease Control and Prevention (CDC) issued new guidelines for prescribing opioids in 2016, little is known about opioid coverage and restrictions under Medicare, which often serves as the standard for other insurers.

For its observational study, the Yale team reviewed prescription drug plan formulary files from the Centers for Medicare and Medicaid Services in 2006, 2011, and 2015. The researchers included data from Medicare Advantage and Part D plans, examining coverage for all opioid medications except methadone.

The researchers found that in 2015, one-third of the drugs were prescribed with no restrictions, such as prior authorization or step therapy. That is down from two-thirds unrestricted in 2006, but still a significant portion had no prescribing limitations, said the study’s first author Dr. Elizabeth Samuels, a postdoctoral fellow in the National Clinical Scholars Program.

While limits in the quantities of pills prescribed did increase over time, the type of dosage restrictions recommended by the CDC only accounted for 13% of prescriptions covered in 2015, the researchers noted.

The study also found a modest increase in coverage of opiates between 2006 and 2015. “An increasing number of opiates were added to the formulary list,” Samuels noted.

Prescribing restrictions can have an impact, the researchers said. A prior study of a private insurer reported a 15% decrease in opioid prescribing when they implemented restrictions, including prior authorization, quantity limits, and provider-patient agreements.

Samuels adds that several states have passed legislation to enact prescribing limitations using formularies. “People are looking for any way to control the increase in opioid-use disorder. This is one strategy,” she said.

Other Yale authors were Joseph S. Ross and Sanket S. Dhruva.