something else noteworthy.
amphetamine psychosis can also be caused by the massive norepinephrine releases that all amphetamines cause. it can become so sever that it reaches the point of an 'adrenal storm' in overdose cases, which means that the victim's heart rate and blood pressure are at or near the maximum possible rate and pressure. this in and of itself causes many symptoms of psychosis, including panic, paranoia, aggression, hallucinations, and delusions. these reactions only further the heart rate and blood pressure, which left untreated, will most likely lead to stroke or heart attack from stimulant overdose.
marijuana's euphoric properties are present because the THC/CBD activate some opioid receptors, but have a lower affinity than most opiates, so the euphoria from weed is not quite as strong as that of opiates, especially full agonists. this is also why weed has painkilling properties, aside from the fact that the psychedelic effects distract from the pain.
i have never heard of a person going into psychosis purely from smoking weed, however, as stated above, weed, along with many other psychedelics, have the potential to aggravate or catalyze a large variety of mental disorders. however, most recreational drugs can have this affect on people whos brains are predisposed to mental disorders. the drugs essentially push the user over the edge into a full blown mental disorder because the drugs tip the very delicately balanced system that is in place. im not sure how else to explain it.
so yeah, thats my take.