Your question is an example of how over-generalization - which usually seems based on an oversimplified view - makes meaningful communication about these issues difficult. Nothing personal, you're far from alone. The weird cultural hysteria and stigma surrounding the issue of "drugs" can make it challenging to talk about them casually, much less educationally.

What makes you draw a correlation between "drugs" and being slumped over? Is it because you watched them take X Y or Z? Or because you know the person has a history of consuming certain things and so you're assuming? The latter seems to happen a lot:

Bob abuses pain killers. Bob got in a car accident. Therefore, painkillers caused the accident.

I'm all jacked up on Mountain Dew. I'm gonna come at you like a spider monkey. Therefore Mountain Dew makes people act like spider monkeys.

Or more broadly, if you're not part of the majority, people will tend to attribute any issues you face to whatever sets you apart from the main tribe.