THC content also will determine the affects to your brain. However, there are numerous reports that do mention there are affects between marijuana use and: Brain structure volume, Quality of white matter,Ability to perform cognitive function all in teenagers. Which is why it is not recommended for anyone under 18 while they are still developing. I personally stay away from it, as I have seen what it has done to several of my friends who have been smoking since high school. They were incredibly smart, now I feel like their brains are practically fried. But then again, some studies suggest there are no permanent affects on your brain. So, who knows.