This has been a regular topic here since 2014.
Oct 2014: 

https://www.theglobeandmail.com/life/health-and-fitness/health/your-kids-brain-on-pot-the-real-effects-of-marijuana-on-teens/article21127612/

https://www.theglobeandmail.com/life/health-and-fitness/health/48-resources-you-should-read-to-understand-marijuanas-effects-on-teens/article21126310/