Possible cart-before-the-horse? Perhaps they have developing schizophrenia, and are using marijuana to self-medicate. I know a person who doesn't smoke pot (or do *any* drug, legal or illegal) but she imagines that over 1000 people are stalking her---people from Amazon, Facebook, her mother's neighbors, her daughter's ex-roommates (who she says are part of a crime cartel), and some "white hats" thrown in for good measure. I also know a person who developed schizophrenia at about 27 years, who treated pot as "medicine". I've smoked pot for many years, off and on (currently off), occasionally heavy usage, and I've never dealt with paranoid delusions. Just weight gain and some short-term memory loss.