Dr. Phil is going against the grain a bit. It seems the consensus is that weed has no lasting side effects. At least that is what weed smokers tell you (when they are coherent). It is now completely legal in a couple of states, and legal for medical use in most states.
But I already knew that weed lowers your IQ, you have only to talk to your old high school buddies who do that stuff to know they aren’t firing on all cylinders (perhaps they never were…). And yes, it is indeed addictive (9%, if I recall…), just not as addictive as alcohol or Heroin (both with addiction rates in the 20-30% range). I know this because I worked counter narcotics for the CIA for a while…)
The violence thing is new to me though, most stoners don’t have the mindset for violence. But then again if they don’t have their week, maybe they do get a bit testy. And if I were to lose some of my current genius, I might get violent too! Read the article if you want more details from Dr. Phil.