I was a teenage hophead.

I'm not conversant with enough statistical analysis and I lack a sufficiently broad familiarity with the relevant body of research to refute this study's controversial conclusions systematically. But I can address the claims of the Duke University study from my own perspective. I started smoking marijuana on a daily basis when I was thirteen. With a few notable and memorable exceptions, I didn't stop smoking it daily until until well into my twenties. During that whole period (1976-1986) I only ceased smoking dope for short periods, when marijuana became unavailable in the community, that is, during what is known as a "drought." I found that when I stopped, there was a certain increase in my cognitive capacity overall, and that my short-term memory and general attentiveness seemd to have been enhanced through abstenance. But it's noteworthy that whatever damage may have conceivably occurred to me pursuant to said chronic cannabis consumption appeared to be a temporary phenomenon. Of course it's possible that I may have diminished whatever potential existed within me to exell in certain endeavors, but I tend to doubt any such potential reduction in brain power stemmed specifically or exclusively from ingesting reefer on a long-term basis. Many other factors could account for the failure on my part to learn the Russian language to the point of being conversant. It might have been the great amount of beer, wine and hard liquor I drank that hindered my progress in Pre-college Algebra. Prescription medication abuse and the consumtion of other psychotropic substances on my part, or a combination of all of the inadvisable practices listed above could be the reason why I dropped out of more than one high school. And I'll extend my contention further, and apply it to the larger society. I've known highly successful computer programmers who smoked some of the most powerful California bud I've ever encountered in my life during their time off. Whether or not they'd been potheads in early adolescence, they weren't hindered as adults in their inordinately complicated and difficult jobs, certainly not as a result of getting high during the weekend. Alternately, I've encountered countless hundreds or thousands of persons who never puffed one single drag off a joint whose level of academic achievement never in their lives seemed to transcend the level of common mediocrity. http://www.boston.com/news/science/2012/08/27/teen-pot-use-linked-later-declines/d25ZcUiFASyet8jEZZDfDI/story.html