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Summer 2010 | Vol 13 No 4

Research update

Mark de la Hey

Early cannabis use may increase risk of psychosis

Cannabis use at an early age significantly increases the risk of psychosis among young adults, according to research from the Park Centre for Mental Health in Wacol, Australia. Researchers studied the relationship between cannabis use and mental health among 3,801 individuals born between 1981 and 1984. Participants were followed for 21 years, at the end of which they were asked about past cannabis use and were assessed for non-affective psychosis, hallucinations and delusions. Sixty-five participants were diagnosed with a non-affective psychosis, such as schizophrenia, persistent delusional disorder or acute and transient psychotic disorders, and 233 endorsed at least one hallucination item on a diagnostic interview. Those who had used cannabis for six or more years were twice as likely as those who had never used cannabis to develop a non-affective psychosis, four times as likely to have high delusion scores, and almost three times as likely to have experienced hallucinations. Within the 228 sibling pairs in the sample, siblings who had been using cannabis for longer periods were more likely to have higher delusion scores. This makes it less likely that the associations found in the study were the result of genetic or environmental influences, since the siblings could be expected to have a common genetic and environmental background.

Archives of General Psychiatry, March 1, 2010, v. 67 (5), doi: 10.1001/archgenpsychiatry.2010.6. John McGrath et al., Queensland Centre for Mental Health Research, Park Centre for Mental Health, Wacol, Australia.