Professor David Nutt: Cannabis does NOT damage the brain, alcohol does - complete with neuro-scans:
https://youtu.be/XFu8W3DqXVg?t=27m34s
https://youtu.be/CebKNmlKTto
https://www.youtube.com/watch?v=2TookjqAqF4

Professor David Nutt:
http://drugscience.org.uk/whatwedo/drugharms

What about The Peter Boris Centre for Addictions Research McMaster University
Cannabis Law Reform in Canada: Pretense & Perils report, from 2017? It talks about the more serious perils: Alcohol, Tobacco and Pharmaceuticals, plus a lot more:

https://fhs.mcmaster.ca/pbcar/documents/Pretense%20&%20Perils%20FINAL.PDF

Neuropsychopharmacology Professor David Nutt mentioned in this London Article talking about Canada and Cannabis May 11th:
https://www.theguardian.com/commentisfree/2017/may/11/mice-benefit-research-cannabis-why-not-us

https://en.wikipedia.org/wiki/David_Nutt