A University of Arizona study on possible benefits of marijuana use for veterans suffering from post-traumatic stress disorder has cleared another hurdle from the federal government.

The U.S. Department of Health and Human Services approved the study, allowing it to proceed to its next step.

UA researchers proposed the study in 2011, and quickly received approval from the Food and Drug Administration.

“We’ve just been waiting three years now for the Public Health Service to give us the green light in order for us to purchase study drug,” said Dr. Sue Sisley, lead researcher on the proposed study. “That’s been the bottleneck.”

Sisley is now awaiting approval from the U.S. Drug Enforcement Agency.

The agency has no timetable for giving its verdict.