The fight to legalize the medical use of marijuana was dealt a blow Thursday when the Food and Drug Administration contradicted an earlier review by the respected Institute of Medicine and concluded that “no sound scientific studies supported medical use of marijuana.” This finding, based on past studies by the FDA and other government health agencies, will further muddy the already confusing messages coming from scientists, doctors and legal agencies. Eleven states have legalized the use of marijuana if prescribed by a physician for medical conditions such as relieving nausea after chemotherapy, and AIDS-related wasting. But the Supreme Court last...