“In the largest longitudinal examination of marijuana use and IQ change, we find little evidence to suggest that adolescent marijuana use has a direct effect on intellectual decline.” The words of real scientists carrying out real research and publishing real reports in the Proceedings of the National Academy of Sciences. The fact that the study involved direct comparisons between identical twins made the evidence produced pretty irrefutable. Not to mention, one-sided – cannabis doesn’t kill your IQ in later life, no matter what they tell you.