That behavior illustrates another aspect of pot use. It precipitates psychotic disorder. I don't think it can be determined yet what the exact connection is--does pot cause it? Does pot induce the disorder to show up faster in people who were going to get it anyway?
In any case, pot causes brain damage, which is apparently permanent.
I think the link has been established between pot and “heightened psychosis” among people who already have psychotic symptoms. I’m not sure it’s been established that pot actually causes psychosis.
Also, I personally would not say pot “causes brain damage” if by brain damage we mean killing brain cells. Alcohol kills brain cells by gluing red blood cells together so that they clump in the capillaries, tear the capillary walls and rupture nearby brain cells in the process.
As far as I have read, pot does not kill brain cells. However the link to short-term memory loss is well established and new studies show the younger the user, the more permanent the effect. I would use the phrase “brain impairment”, not “brain damage”, since to me that second phrase implies destruction of brain cells.
Also, I don’t know what studies there are regarding productivity, but my own non-scientific observation of pot-heads leads me to believe that pot has dramatic negative effects on productivity.