[SOLVED, SEE BOTTOM]
Simply put, I cannot administer Go-Juice or any other non-recreational drugs to a prisoner in my colony because it is against their religion; my religion does not forbid it.
It can be recreated by attempting to administer a drug via the 'operations' menu on a prisoner that believes in a religion that forbids drug use.
I have a greyed out "Cannot operate on [prisoner]: Ideoligion forbids" when I attempt to tell a doctor to carry on with the operation.
Realistically, what's to stop me from forcing drugs down a prisoner's mouth? It would make sense if my religion forbade the use of drugs, but in this world it does not.
I can supply a save file if necessary, please let me know if there's any more information needed.
SOLVED; turns out hard drugs were in fact banned by my religion, I did not realise 'social and medial' drugs was ticked. The fool I am! I shall now delete this post. I am leaving the edit here for moderators in case.