I know a guy who was fairly smart and decided to take LSD at university in his "teaching assistant" room, and make notes about his experience. Something went wrong during his trip and he ended up confronting some kind of demons. Previously purely rational person within a year switched to become a seventh-day adventist. Since then I simply couldn't trust his judgement anymore; not because he became religious, but because something really damaged his brain on his first trip.

Another person I knew was a brilliant winner of math and informatics Olympiad. Decided to try heroin once. Dropped out of university the following year, spent a year working in construction, went to a lesser university, dropped out after two years. A talent gone.

Some drugs ("krokodil", meth), seem to give pretty brutal feedback about their use, e.g. literal zombification of humans. There are so many horrible stories...

It's really complicated as a human has to go against their own nature to override brain's pleasure complex, often also against their friends, tribe, customs etc. while the whole world keeps saying: "Just take it, it's normal, everything will be fine", and 10 years later finding themselves one step from abyss. I would rather convey a strong message: "It's not OK, don't ever do it!"