The only person that was likely doing K was Kayla. I've watched people shoot it up and it's not really a party drug. Depending on the dosage, which I promise they were not being careful with, you basically just lose all motor control and slump over, frequently it sounds like you are struggling to breathe as you disassociate and experience... I dunno. Ego death?
Ketamine therapy is very highly affective to very specific types of depressions and ptsd when administered correctly over an amount of time determined by many facots. It is also an extremely interactive drug, if you are investigating ketamine for fun or therapy one of the first things you will find out is if you mix K with literally anything else you will very literally melt your fucking brain in your skull. An alcoholic party drug user like Nick and his demon whore pet aren't interested in passing out and disassociating and experiencing a new type of truth that human language cannot convey, they want to fuck. Kayla uses it to cope with the reality that she's the tossed away used up toy and has nowhere else to go and it's kind of her fault (to be fair I am not victim blaming, she has friends and family pleading with her to leave and she hasn't).