if you find someone who actually decides to do drugs, inject them with hallucinogen, than tie them up and force them to watch something like Excel Saga, just to teach them drugs are bad the hard way.
But in all seriousness, certain drugs could in fact kill you, even the one's prescribed by a doctor. Let's see, Methonaul, if even a little bit over the amount is taken can cause you to start throwing up blood and has a hi chance of killing the user. Cocaine has a mix of effects, Marijuana isn't bad, it's just illegal. Let's see, a few other bad drugs are things like Adrenocrome (it's made from a human adrenalin gland) it tends to have a worse reaction than speed to where everything tends to quicken to such a degree that your heart could literally explode and it could even cause hallucinations. I'm trying to remember some other drugs that should never be used under any circumstances, but I think I posted some of the worst stuff I've ever had to study and have seen the effect of on others.