I note what you are making the distinction is with kids. it doesn't hurt adults, but it has been shown to harm still DEVELOPING brains. I'm surprised the adult smoker replies are missing this important distinction. Be 18, smoke all you like, who cares? yes you probably have high function even while high.
but it has been shown to cause physical abnormalities with still developing brains of young people, especially if they begin in very early teenage years. While we hate the media, and we hate pharma, not all researchers are nwo.
For young users, even those who smoked one joint per week, the nucleus accumbens and amygdala showed changes in density, volume and shape. The scientists also discovered that the more pot the young people smoked, the greater the abnormalities observed from neuroimaging.
Bottom line? young people should hold off as long as possible. then have it!