Just an anecdotal tale of personal experience in response to those who maintain that cannabis inhibits cognitive abilities...
In the early 70's when I was pursuing my undergraduate studies, the professor of a physics course I was taking was infamous for inflicting outrageously challenging exams, which consisted of a near-impossible mix of formula-based and essay questions, on his students. (At the time, even 4-function calculators were quite expensive, so their use during exams was forbidden.) Instead of a midterm and final, as was the university norm, he administered four exams during the semester, which all counted equally toward 80% of each student's course grade, with the remaining 20% determined by weekly lab quiz performance. No one ever finished one of his exams early, and no one ever scored 100%. Ever.
I spent a great deal of time preparing for the 2nd or 3rd exam - don't recall which, because I was having difficulty assimilating the material that would be covered, and was afraid I was going to bomb the test. On the morning prior to the test, I still just wasn't getting it. It was nearly time to leave for the exam. Finally, I resigned myself to absorbing the grade hit and decided to at least take the exam in a better frame of mind, so I smoked a fattie of fresh Acapulco Gold before leaving for the lecture hall.
To my surprise, answers to the test questions came easily to my mind. Whether those answers were correct or not remained to be seen. I finished the 50-minute exam 10 minutes early and left, wondering how badly I had done. I was again surprised when the professor handed back the graded exams and announced that there had been exactly one perfect score. It was mine!