kids is a cool film, but not much of a cautionary tale. it's more like a 90s urban euphoria, in that the message is really more to adults: "this is what teenagers are actually doing right now".

what (imo) would make requiem for a dream really effective is that it shows the transition from the "honeymoon phase" of drug use to the "consequences phase" really well. I think this is the part that teenagers really don't understand (or at least I didn't). when you're starting out, it can seem like a lot of the anti-drug messaging is just fear mongering (and it is, to an extent). but most people that age don't yet have the perspective to distinguish between harmless fun and a slow motion crisis.

trainspotting is also great, and a bit more realistic than requiem for a dream. but if I had to pick one of the two to show to teens, I'd probably pick the former.