This month, the F.D.A. surprised the researchers behind a proposed study to assess the safety and efficacy of using marijuana to treat military veterans with post-traumatic stress disorder, and other experts in the field, by authorizing the trial to proceed, according to an F.D.A. letter obtained by The New York Times.  The decision was a rare instance in which the F.D.A. has permitted smoking marijuana for a study looking at the therapeutic benefits of the plant, rather than its harms.  Read the article here.