Cannabis Use Associated With Psychosis
Young adults who have used cannabis or marijuana for a long period of time are more likely to have hallucinations or delusions or to meet the criteria for psychosis, according to a report posted online that appears in the May print edition of Archives of General Psychiatry, one of the JAMA / Archives journals.
Previous studies have found an association between cannabis and psychosis, according to background information in the article. However, concerns remain that this research did not adequately account for confounding variables.
John McGrath, MD, Ph.D., FRANZCP, of the Queensland Brain Institute, University of Queensland, Australia, and colleagues studied 3801 young adults born between 1981 and 1984. In a 21-year follow-up, when participants were an average age of 20.1, were asked about cannabis use in recent years and assessed using various measures of psychotic outcomes (including a diagnostic interview, an inventory of delusions and items to identify the presence of hallucinations).
A 21-year follow-up, 17.7 percent reported having used cannabis for three or fewer years, 16.2 per cent of four to five years and 14.3 percent for six or more years. A total of 65 study participants received a diagnosis of “non-affective psychosis, including schizophrenia, and 233 had at least one positive element in the hallucination of a diagnostic interview.
Among all participants, a longer duration since first using cannabis-related psychosis was associated with multiple outcomes. “Compared with those who never used cannabis, young adults who had six or more years since the first use of cannabis (ie, begun to use, when about 15 years or younger) were twice as likely to develop non-affective psychosis and four times more likely to have high scores on the Peters et al Delusions Inventory [a measure of illusion], “the authors write. “There was a” dose-response “relationship between the variables of interest: the greater the duration since first use of cannabis, the greater the risk of psychosis related to the results.”
In addition, researchers assessed the association between cannabis use and psychotic symptoms in a subgroup of 228 sibling pairs. The association persisted in this subgroup, thus reducing the likelihood that the association was due to shared unmeasured genetic and / or environmental influences, “the authors continue.
“The nature of the relationship between psychosis and cannabis use is not simple,” they write. Individuals who had experienced hallucinations early in life were more likely to have used cannabis and to use it more often. “This demonstrates the complexity of the relationship: persons who are vulnerable to psychosis (ie, those who had isolated psychotic symptoms) were more likely to initiate the use of cannabis, which subsequently could contribute to an increased risk of conversion a non-affective psychotic disorder. ”
The results should encourage further research to elucidate the mechanisms underlying the relationship between psychosis and cannabis use, the authors conclude.
This work was funded by the National Health and Medical Research Council of Australia. Co-author Dr. Alati is funded by a National Health and Medical Research Council Career Development Award in Population Health.
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