[derlvative]

This is a good point. Doctors can prescribe drugs approved for disease X off label to treat disease Y even when effectiveness against Y has not been proven. In this case, the drug has not been approved for any disease so it can't be prescribed. Just goes to show how arbitrary the rules are.

[radlad]

I'm not sure that makes it "arbitrary." Approval is not just about effectiveness but also risks and side effects.

[JumpCrisscross]

If we've gotten to Phase III, the risks and side effects are understood as well as they would be for a doctor prescribing off label. While I might not call it arbitrary, I would say it's an unappreciated edge case.