Long term marijuana use linked to 'psychosis'
POSTED March 2, 2010 - 15:12 | POSTED BY Abby Kapoor
Last edited by Kangna Agarwal on March 2, 2010 - 16:23
Lead author of the study, Dr. John McGrath, MD, PhD, FRANZCP, of Queensland Brain Institute (QBI), University of Queensland, Australia, and the team studied 3,801 people born in Brisbane, Australia between 1981 and 1984 and questioned them when they reached the age of 21.
Researchers asked subjects about their drug use in the past. By using various assessment measures they assessed psychotic outcomes, such as delusions, and items identifying the presence of hallucinations.
They even looked at marijuana use and psychosis symptoms among siblings in order to make sure they were not missing a genetic or environmental factor.
Outcome of the study
At the 21 year follow up questioning, nearly 18 percent admitted smoking marijuana for three years or less, 16 percent said they smoked for between four and five years, and just over 14 percent reported using cannabis for six or more years.
Overall, 65 study subjects were diagnosed as suffering from schizophrenia, while 233 had at least one positive item for hallucination in the diagnostic interview.
Dr. McGrath said, "Compared with those who had never used cannabis, young adults who had six or more years since first use of cannabis were twice as likely to develop a non-affective psychosis and were four times as likely to have high scores on the Peters et al Delusions Inventory - a measure of delusion."
"There was a 'dose-response' relationship between the variables of interest - the longer the duration since first cannabis use, the higher the risk of psychosis-related outcomes," he added.
Link between psychosis and marijuana use
The scientists cautioned that while the relationship between psychosis and drugs use "is by no means simple," teens who had experienced hallucinations early in life were more likely to have used cannabis for longer duration and more frequently.
The findings of the study were released on Monday, March 1, 2010, and published in the journal Archives of General Psychiatry, one of the JAMA/Archives journals.
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