I really don't see how they could make posession of it illegal since as u say it's only oil. I'd guess that the administration of it to patients is illegal for anyone not certified.
Personally I don't understand why anyone would use it tho. Not flaming here. If u want it I have no issues with that but thinking of having an implant for intsance: A nonfunctional lump on top of my real muscle gives me the creeps. I feel like that with synthol.