A new study finds the percentage of benzodiazepine prescriptions written for outpatient medical visits doubled between 2003 and 2015. The benzodiazepine visit rate doubled from 3.8 percent to 7.4 percent of visits.

Half of those prescriptions were written by primary care doctors, NPR reports. Benzodiazepines include Xanax, Valium and Ativan. Although they are most often prescribed for anxiety, insomnia and seizures, the researchers found the largest increase in prescriptions was for back pain and other kinds of chronic pain.

Benzodiazepines are recommended for short-term use, but the study found an increase in long-term use.

“I don’t think people realize that benzodiazepines share many of the same characteristics of opioids,” study co-author Dr. Sumit Agarwal of Brigham and Women’s Hospital in Boston said. “They are addictive. They cause you to have slower breathing; they cause you to be altered in terms of mental status. And then, eventually, [they] can cause overdose and deaths.”