Lynn Zimmer, PhD, late Professor Emeritus at Queens College, noted in her 1997 book Marijuana Myths, Marijuana Facts:

“Given that the incidence of schizophrenia declined substantially in Western societies in the 1970s, at the same time cannabis use was rising, it seems highly unlikely that marijuana causes schizophrenia in otherwise healthy people….

Cannabis psychosis is self-limiting, disappearing in a few days with or without medical treatment. Toxic psychosis probably occurs more commonly in individuals with preexisting psychiatric disorders….

Marijuana temporarily alters mood, thought, emotions, and perception, sometimes quite dramatically. None of marijuana’s effects cause people to behave in any particular manner. In the midst of a toxic psychosis, people may become agitated and frightened. In response to acute panic, people may become withdrawn and inactive. Neither of these states eliminates the social and moral restraints that guide human behavior.”