In case they question your source, here is another one:
The AHA released two new studies on Monday that found that daily marijuana use can impact both brain and heart health
www.yahoo.com
I have a family member addicted to chain smoking cannabis and who has never smoked tobacco. She is still in her 50's but has developed COPD, has scarring on her lungs and observable cognitive impairment.
As more and more states legalize cannabis for recreational use I suspect we will see more of this kind of damage. Is smoking cannabis less likely to cause irreversible harm to the body than tobacco? I don't know. I think the studies show cannabis to be less addictive than tobacco but it definitely can be addictive. But for sure we cannot say it is harmless and it certainly isn't healthy. And unlike tobacco, cannabis can impair judgment, reaction time, coordination, ability to concentrate or focus.
Note: A direct link between marijuana use and lung cancer has been elusive. But there is a direct link between marijuana use and lung scarring. And scarring of the lungs is definitely linked to a higher risk of developing lung cancer.