So, precisely the wrong approach would be to block research of any kind by continuing the severe prohibition of these substances.
Perhaps we need a new category of prescription, e.g. "for use only under direct supervision of a qualified medical professional" In other words it could be dispensed in a clinical setting, but not via a pharmacy or other "take home" pathways. I'm thinking that must already exists for certain surgical anesthetics, etc.
https://en.wikipedia.org/wiki/List_of_Schedule_I_drugs_(US)
https://en.wikipedia.org/wiki/List_of_Schedule_II_drugs_(US)