The federal government has finally approved a small-scale clinical study that would examine marijuana's effectiveness in treating post-traumatic stress disorder in veterans, The Independent reported.

The Department of Health and Human Services' (HHS) decision surprised researchers and is being hailed as a "major victory," and a major shift in U.S. policy, The Independent reported. Marijuana advocates have struggled for decades to secure approval for research into marijuana's medical uses.

The research proposal from University of Arizona was approved by the Food and Drug administration long ago, but the entire project was stalled because the HHS had not approved the purchase of the medical marijuana needed for the study.

The federal agency cleared the purchase of medical marijuana by the studies' chief financial backer, the Multidisciplinary Association for Psychedelic Studies (MAPS), which supports medical research and legalization of marijuana and other drugs.

"MAPS has been working for over 22 years to start marijuana drug development research, and this is the first time we've been granted permission to purchase marijuana from NIDA," the Boston-based group said in a statement.

According to MAPS, the federal government has never before approved medical research involving smoked or vaporized marijuana.

A spokesman for the group told the Associated Press t organizers have called off a protest over the stalled study that was planned for later this year.

The study, which will be conducted by researchers from the University of Arizona, will measure the effects of five different potencies of smoked or vaporized marijuana in treating symptoms of PTSD in 50 veterans.

People with PTSD suffer from anxiety attacks, flashbacks, and depression. Physicians have long speculated that medical marijuana use would help to calm the parts of the brain affected by PTSD.