Medicare has not put significant restrictions in place for opioid prescriptions, despite recent government guidelines that recommend such limits, according to a new study.

Yale researchers analyzed Medicare coverage for opioids. They found that in 2015, one-third of opioids were prescribed with no restrictions, such as prior authorization or setting quantity limits, HealthDay reports.

The study, published in Annals of Internal Medicine, also found a modest increase in Medicare coverage of opioids between 2006 and 2015.

In 2016, the Centers for Disease Control and Prevention issued guidelines that recommend primary care providers avoid prescribing opioid painkillers for patients with chronic pain. The guidelines state that doctors who determine that opioid painkillers are needed should prescribe the lowest possible dose for the shortest amount of time.