title: A controlled family study of cannabis users with and without psychosis.
abstract: BACKGROUND
  Cannabis is one of the most highly abused illicit drugs in the world. Several studies suggest a link between adolescent cannabis use and schizophrenia. An understanding of this link would have significant implications for legalization of cannabis and its medicinal value. The present study aims to determine whether familial morbid risk for schizophrenia is the crucial factor that underlies the association of adolescent cannabis use with the development of schizophrenia.
  
  
  METHODS
  Consecutively obtained probands were recruited into four samples: sample 1: 87 non-psychotic controls with no drug use; sample 2: 84 non-psychotic controls with cannabis use; sample 3: 32 patients with a schizophrenia spectrum psychosis with no drug use; sample 4: 76 patients with schizophrenia spectrum psychosis with cannabis use. All cannabis using subjects used this drug during adolescence, and no other substance, with the exception of alcohol. Structured interviews of probands and family informants were used to obtain diagnostic information about probands and all their known relatives.
  
  
  RESULTS
  There was an increased morbid risk for schizophrenia in relatives of the cannabis using and non-using patient samples compared with their respective non-psychotic control samples (p=.002, p<.001 respectively). There was no significant difference in morbid risk for schizophrenia between relatives of the patients who use or do not use cannabis (p=.43).
  
  
  CONCLUSIONS
  The results of the current study suggest that having an increased familial morbid risk for schizophrenia may be the underlying basis for schizophrenia in cannabis users and not cannabis use by itself.
authors.affiliation: Harvard Medical School, 25 Shattuck St, Boston, MA 02115, United States.
authors.forename: Ashley C
authors.initials: AC
authors.lastname: Proal
authors.affiliation: Harvard Medical School, 25 Shattuck St, Boston, MA 02115, United States; Veterans Administration Boston Healthcare System, 940 Belmont St, Brockton, MA 02301, United States.
authors.forename: Jerry
authors.initials: J
authors.lastname: Fleming
authors.affiliation: Harvard Medical School, 25 Shattuck St, Boston, MA 02115, United States; Veterans Administration Boston Healthcare System, 940 Belmont St, Brockton, MA 02301, United States.
authors.forename: Juan A
authors.initials: JA
authors.lastname: Galvez-Buccollini
authors.affiliation: Harvard Medical School, 25 Shattuck St, Boston, MA 02115, United States; Veterans Administration Boston Healthcare System, 940 Belmont St, Brockton, MA 02301, United States. Electronic address: Lynn_DeLisi@hms.harvard.edu.
authors.forename: Lynn E
authors.initials: LE
authors.lastname: Delisi
mesh_terms: D005190:Family; D005192:Family Health; D005260:Female; D006801:Humans; D008297:Male; D002189:Marijuana Abuse / Q000150:complications* / Q000175:diagnosis / Q000453:epidemiology*; D011618:Psychotic Disorders / Q000150:complications / Q000175:diagnosis; D012307:Risk Factors; D012559:Schizophrenia / Q000150:complications* / Q000175:diagnosis / Q000453:epidemiology*