Should I be stopping people who slip something into their own drink?

i've been bartending for 7 years (2 in Pakistan and 5 in the U.S.) and i've honestly never seen something like this before. last month, this guy came in around 7pm on a Friday and ordered a gin and tonic. he sat at the bar but he didn't make any talk-- perfectly fine by me as an extremely introverted tender. as i was serving another customer, i saw the guy out of the corner of my eye. he had pulled down his sleeve to the palm of his hand and was clearly subtly pouring something into his own drink. it happened very quickly so i couldn't be sure of what i saw. i just kept an eye on him to make sure he wasn't giving his drink to anybody.

he didn't. he just sat there and drank. he seemed to get incredibly drunk by the time he finished just half of his drink, he was looking at the TV behind the bar, but not the one playing football; instead, the one cycling through advertisements for our bars coming events (karaoke wednesday, flashy friday, etc.). he was drooling a little bit, too. honestly, as a previous dive bartender, it wasn't behavior you haven't seen every single friday night of your goddamned career: an old loser come to the bar to sit alone and look wretchedly pitiful. but i'd never seen someone roofie themselves before, and i was pretty sure that was exactly what was happening there

i dont know what happened that night cuz i got off my shift just then. i passed along a warning to my replacement and forgot about it. but two weeks ago, i saw the same thing happen. it was a younger dude this time, and he was not alone but at a table with a couple friends. i saw him across the bar slipping in something into the drink next to him. i thought he was roofying the drink of the girl next to him, but then he took a big old swig out of the cup he had just spiked. jesus christ, i thought, another self-roofier??? And that dude ended up passing out later during a game of darts and had to be carried out by his friends.

And just now my coworker was telling me that they had seen someone do it again last night. she said she kept an eye on the guy all night to make sure he was the only one drinking it. i asked her if she thought we should stop these people from roofying themselves and she said no. she said "people take rohypnol recreationally and we let people vape and hit their dab pens in here so its no different." im not sure if i agree with that. for one, having a roofied cup in a bar is a risk even if it is a self-roofie. for example, what if the self-roofier leaves the cup on a table half-finished and some other drunk jackass drinks from it? or what if they get too "high" and start becoming a problem?

what do you guys think?