There has been a recent study that smoking pot in the developing years can lead to a bit of mental strife. I originality read this article on bbc,
Here is an article on itg
However, I really doubt that the research is completely unbiased.
I don't believe it's a wise idea to let teenagers have drugs and alcohol, since there's a lot we don't know on how brains develop in that time.
Other then that, I live in a house of daily smokers, and hang out with a lot of friends who smoke a LOT.
They're great people.
It's pretty easy to come by here, it doesn't feel illegal.
Though, the second we legalize weed, the potheads will have nothing to talk about. Haa haaaa.