Marijuana

For its study, Northwestern University examined daily marijuana users who began at age 16 or 17 (and used marijuana for a period of three years) and pitted those individuals against same-age young adults that had never used marijuana. Researchers then examined MRI scans that focused on the area of brain responsible for long-term memory retention, the hippocampus. To attempt to be as fair as possible, researchers conducted these MRI scans on subjects in their early 20s who were two years removed from their heavy marijuana use. The findings of the study showed an oddly shaped hippocampus in heavy marijuana users accompanied by an average long-term memory test score that was 18% lower than young adults who'd never used marijuana before. This odd formation was not observed in the non-user group. As senior author Dr. John Csernansky stated, "The memory processes that appear to be affected by cannabis are ones that we use every day to solve common problems and to sustain our relationships with friends and family." Also noted, this was the first study to confirm a link between heavy marijuana use and a misshapen hippocampus that led to poor long-term memory performance. This study comes on the heels of a 2013 study released by Northwestern University that suggested heavy marijuana users' short-term memory may be affected because of abnormalities in heavy users' sub-cortex.

https://www.psychologytoday.com/blog/your-brain-food/201106/does-it-matter-when-you-start-smoking-marijuana

http://www.cnn.com/2014/01/28/health/time-teens-pot/

http://www.cnn.com/2013/12/16/health/time-marijuana-brain/index.html

http://www.amenclinics.com/blog/marijuana-causes-long-term-brain-changes/

http://www.amenclinics.com/blog/marijuana-and-brain-changes-part-2/