Just one-third of substance use treatment facilities in the United States offer monthly injections of long-acting buprenorphine, according to a new study.

Long-acting buprenorphine, approved by the Food and Drug Administration in 2017, is given as a monthly in-person injection. This may be preferred by some patients and clinicians because it avoids the necessity of taking a daily pill, researchers at the University of Chicago said. Like other medications used to treat opioid use disorder, long-acting buprenorphine faces restrictions from the Drug Enforcement Administration. This may limit its widespread use, the researchers wrote in the Journal of the American Medical Association.

The study found primary care physicians are more likely to offer long-acting buprenorphine injections than treatment centers, HealthDay reports. This may be because doctors’ offices have fewer regulatory and administrative obstacles to prescribe the medication as a monthly injection, according to the researchers.

“The takeaway is, we still have a lot of work to do to make the full complement of opioid treatment options available to patients,” researcher Dr. Samuel Bunting said in a university news release.