The "finding" that cannabis has no medicinal value was specious from the outset. Cannabis tincture was part of western pharmacology when the first federal regulation was enacted during FDRs administration. It was declared to have no medicinal value in the 70's based when the Controlled Substances Act was passed, based on testimony that there were no ailments that it was prescribed for. But the reason it wasn't prescribed is that the Marijuana Tax act had made it effectively unobtainable for the last 30 years.
Which is one reason they banned it under its Mexican name of "marihuana".