The problem with this study is that they didn't explore external factors in the patients lives that lead to cannabis use/abuse at an early age. What leads a youth to begin using cannabis at an early age to begin with? Are they struggling socially? Do they experience loneliness and isolation due to family problems or social problems and then turn to the outcasts and indulge in cannabis for acceptance? Correlation in this study doesn't beget causation unless they can account for the external factors that lead to early use. If you want to stop kids from using cannabis it should be regulated like alcohol first, then the factors leading to early use should be examined. It's hard to believe that the small sample size of 30 early and heavy users are well adjusted kids with good family and social lives who just somehow found a bag of grass on the sidewalk and became heavy users. Let's try again. Also, nobody under 21 should use cannabis unless it is to treat a medical condition. We need a fair look that explores more than just one factor.