You do appear to be making them aware from a position of ignorance. I don't take drugs but know plenty who do and they are perfectly normal, functioning human beings. You probably know loads and don't even realise.Well ultimately I can only make sure that they understand the dangers of such substances but once they are over 18 its out of my hands. i can only hope that I've done a fair job in making them aware of the dangers.
Your assumption that they aren't available in your town is ludicrous. You won't notice it because people don't turn into drug addled zombies at the first sight of a spliff. Like alcohol, done in moderation certain drugs are perfectly harmless.
I don't particularly care one way or the other but both extremes of the legalisation argument are dangerous. Just saying all 'drugs' are bad is lazy, ill thought out and probably counter productive.