Many doctors who are allowed to prescribe buprenorphine to treat opioid addiction are treating many fewer patients than they could be, a new study finds.

More than 20 percent of doctors who have government waivers to prescribe buprenorphine treated three or fewer patients, and fewer than 10 percent treated more than 75 patients, NPR reports.

The study, published in the Journal of the American Medical Association, was conducted when doctors were allowed to treat up to 30 patients at a time for the first year, and then up to 100 patients after that.

This summer, Secretary of Health and Human Services (HHS) Secretary Sylvia Burwell announced doctors will now be able to treat up to 275 patients if they have additional credentialing in addiction medicine or addiction psychiatry from a specialty medical board and/or professional society, or practice in what the HHS deems a qualified setting.