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.

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.

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.