An Oklahoma doctor who treats patients with opiate addiction by prescribing buprenorphine says federal restrictions on the number of prescriptions he can write for the drug are hurting patients.

The Tulsa World reports that under the Drug Addiction Treatment Act of 2000, doctors can only treat up to 100 patients a time with the drug, which is marketed as Suboxone.

Dr. William Yarborough, an internal medicine specialist at the University of Oklahoma-Tulsa, told the newspaper that he would like to be able to treat more patients with the drug. “I have people out there sick on heroin and other things, and I can’t do anything to help them because I don’t have any slots left,” he said. Dr. Yarborough noted that many of the patients he treats for opiate addiction with buprenorphine are middle and upper class, including lawyers, teachers and other doctors.