The terrible truth about cannabis: Expert's devastating 20-year study finally demolishes claims that smoking pot is harmless

A definitive 20-year study into the effects of long-term cannabis use has demolished the argument that the drug is safe. Cannabis is highly addictive, causes mental health problems and opens the door to hard drugs, the study found.
http://www.dailymail.co.uk/news/article-2783111/The-terrible-truth-cannabis-Expert-s-devastating-20-year-study-finally-demolishes-claims-smoking-pot-harmless.html