While not nearly as over-the-top as the film, Berenson certainly exaggerates suggestions that marijuana can cause psychosis.
Drawing on the 2017 report of the National Academy of Sciences, Engineering, and Medicine on "Health Effects of Cannabis and Cannabinoids: The Current State of Evidence and Recommendations for Research," he directs attention to its conclusion, in Chapter 12: "There is substantial evidence of a statistical association between cannabis use and the development of schizophrenia or other psychoses, with the highest risk among the most frequent users." Berenson admits in a January 4 Wall Street Journal column based upon his book, "None of these studies prove that rising cannabis use has caused population-wide increases in psychosis or other mental illness, although they do offer suggestive evidence of a link." Indeed. But correlation is not causation. And there is always the question of "which came first–the chicken or the egg?" Some schizophrenics might be using cannabis as a form of self-medication.