I've smoked a lot of weed in my time, it never did me any harm. also dabbled with other stuff, which I could see was possibly dangerious (ie, it takes control of when you take it, rather than it being a rational choice) so I left it alone.
did have a night of the whizz recently, which taught me that I am too old! 3 weeks before I was back to normal. had all sorts of horrible after effects.