Personally I just don't see the appeal of anything mind-altering by and large. I admit, if I got the chance to, say, do some weed or acid just once with no legal repercussions, I'd probably go ahead with it just out of an intellectual curiosity (only, though, were it not smoked weed- inhaling smoke is something I will never, ever do voluntarily). Personally, I can throw up enough thoughts to entertain myself, can find other routes of non-self generated occupation, and so on.
That and one of my personal pillars of belief is that one should experience the world for what it is, as is, with unclouded mind/judgment if at all possible.
And last bit, save weed/salvia, every recreational drug has some negative effect- addiction, health problems, etc (and weed has the health problem if you smoke it). And weed is, unfortunately, pretty illegal in most places here in the grand old freedom-restricting, historically anti-freedom United States (some places put people away for up to ten years for possession/use of weed. And they also put murderers away for ten years). Salvia is, in most places, becoming illegal. And as I have a mild paranoia of being caught, mixed with a much more substantial respect for the law in general (in theory, law exists to keep order, and I feel that the whole establishment of law must be respected- not just individual laws- to achieve that).
So basically, because I can feel good enough without the use of/need for drugs to not warrant them on that ground; I can entertain myself both with only my mind or with external things to an extent that ultimately that's all I need; one of my core beliefs is that the world should be viewed and experienced as is, learned and known as is, with no warp whatsoever of perspective; mild paranoia and more substantial respect for the law in general that prohibits drug usage (and as I'm under 21, that would include alcohol for me).
I generally don't care about other people doing drugs, though, so long as A) it has no bearing on me, B) they're not seriously hurting themselves as a result, C) they keep it to themselves, I.E. don't brag about it or do it around me or try to get me into it (admittedly probably unlikely on the last bit).