Well, I think that using any substance that has an intoxicating effect on the user should be used in moderation if not, at all. Be it alcohol or cannabis or any of those nasty hard-core "deathead" drugs. Its a fact that alcohol kills brain cells. I would not be surprised if cannabis intoxication had the same effects to a certain extent. If it is not recommended that individuals who's brains are still in their developmental stages be consuming excessive amounts of alcohol, then cannabis intoxication should be held in the same regard as alcohol intoxication. HOWEVER; I have many friends. Some who started smoking in highschool and some who started smoking in CÉGEP (college). I can say for certain, some were thick as a brick in HS, and believe me, it hasn't improved. Some were straight A's in HS and are now studying applied sciences and calculus. Some started smoking in HS and now just hang around metro stations trying to sell drugs to people. Some are graduating with arts and music degrees. And me? I'm in engineering. To conclude, I believe that cannabis abuse can and likely WILL lead to a noticeable decrease in cognitive functions IF used irresponsibly, excessively and/or during the brain's stages of development (be it pre- or post-natal.) /rant