Could be any of those substances, although personally I find alcohol is kind of the worst one for that type of session. The only time booze really worked out for me the sub was a suuuuuuper lightweight (i.e., got pretty tipsy off half a water bottle's worth of OJ and peach schnapps) and it was a 4 hour long hypno session.

Most of my forced intox guys are into hypno, and the drugs do help them reach that altered state. Forced intox fits very nicely with mind control fantasies, since it's about the dominant taking control over the sub's internal state.

I have one client who love being told what a horny idiot he is and the weed makes him both hornier and dumber, so that works out perfectly for him. Another loves to huff poppers off my pantyhose, literally getting high off my feet.

Some drugs can also enhance your ability to take pain. Poppers relax your asshole, which can help with strap-on. TBH I think some guys just like to party in session and making it part of the play allows them to do so without affecting the dynamic.