http://well.blogs.nytimes.com/2013/12/18/growing-marijuana-use-among-teenagers-spurs-concerns/?_r=0 Removing the bias, such as the suggestion that MJ causes changes in developing brain matter supported by an obviously flawed study (not saying it's not possible, just that a better study should be conducted to prove the hypothesis), this article puts some numbers behind how the increase in MJ use is correlated with a decrease in alcohol and cigarette use in teens. The (ny)times are a'changin.