UK expert’s devastating 20-year study finally demolishes claims that smoking pot is harmless

^  One in six teenagers who regularly smoke the drug become dependent
^  It doubles risk of developing psychotic disorders, including schizophrenia
^  Heavy use in adolescence appears to impair intellectual development
^  Driving after smoking cannabis doubles risk of having a car crash
^  Study author said: ‘If cannabis is not addictive then neither is heroin‘.