I smoked pot for the first time at age 23. I never experimented with drugs in my youth but did become a heavy drinker. I guess I am not normal in that aspect but I was always trying to look out for my future (knowing how many doors a pot conviction would close in the white collar world).
Anyways I have a member of my family who habitually smoked pot from about age 15 to age 17. From 17 to 18 he had been caught a few times and was only doing it occasionally. Recently his court ordered counselor recommended that he be taken to a psychiatrist for some paranoia issues. At this point I think he had just passed a piss test so it had to have been at least a few weeks since he smoked (barring him using a detox kit). So the psychiatrist uncovers some symptoms that was hiding (because even though he thought these things, he knew they were crazy). She gave him heavy anti-psychotics and they almost committed him (he was about like the guy from "Beautiful Mind" but hiding it really well.
The psychiatrist told his mom that chances are good that the habitatual pot use played a major factor in this. She never came out and said "marijuana made your kid crazy", she basically said that it magnified the problem big time. While I personally am still sifting though all the propaganda coming out of the UK about how "super-skunk" turns perfectly normal people into schizophrenics, I can say that as a layperson I don't think more chemicals are good on an adolescent's developing body.
So this kid is 18 years old and looking at quite possibly a LIFETIME of medication and a battle inside his own head. So if any of you are under 18 and smoking, just think about it and do a little research, mental illness is very, very serious.