if you smell/see it, ask where they got it. tactifully, make friends with them. don’t sound like or be like a pig/snitch.
iirc the chinese use it as a sleeping aid, but they are not fond of druggies because of that whole opium thing. ymmv depending on where you are, don’t be dumb.
respect your intuition. if you are not confident with it, just fucking don’t.