The move marks a rare action by the FDA to sanction a study on cannabis despite the plant’s current Schedule I classification under federal law as a drug with no therapeutic use, in the same category as heroin and LSD.

The decision is the latest sign that federal health officials want more research on medical marijuana as its use grows.

More than 300 veterans diagnosed with post-traumatic stress disorder will take part in a five-week study approved by the Food and Drug Administration to examine the effects of smoking cannabis on symptoms from the illness.

The Food and Drug Administration (FDA) this week authorized a long-delayed clinical trial to test whether smoking marijuana can be used to treat post-traumatic stress disorder (PTSD) in veterans.

After a three-year negotiation, the FDA has dropped its objection to allowing patients to self-titrate dosing of smoked cannabis. But regulators want to see additional information about the device that will be used for inhalation.

The Multidisciplinary Association for Psychedelic Studies (MAPS) said this week the U.S. Food and Drug Administration approved a study of the therapeutic value of cannabis on 320 veterans with moderate to severe post-traumatic stress disorder (PTSD) after a three-year effort.