Teenagers who are longtime marijuana smokers are at an increased risk of developing psychoses, such as schizophrenia, hallucinations and delusions, compared to short-term smokers or those who have never smoked pot, a new research suggests.
Scientists at the Brain Institute at the University of Queensland, Australia, tracked 3,801 young adults with the ages between 14 and 21 years. The participants and their mothers were asked about their mental health record and whether they had used any drugs, specifically marijuana, and then evaluated to determine if they had developed any psychotic conditions.
According to the data provided: 17.7 per cent of participants reported smoking marijuana for 3 or fewer years; 16.2 per cent smoked pot for 4 to 5 years; 14.3 per cent reported using marijuana for six or more years. The findings showed that overall, from all the test subjects, those who had started smoking marijuana before the age of 15 years, were more likely to develop symptoms of psychosis by the time they turned 21 years old.
Of the individuals who had smoked pot at an early age, 3.9 per cent had developed a psychotic disorder. This compared with approximately 3 per cent of those who had started smoking marijuana after age 15, and 2.1 per cent of young adults who had never used cannabis. The experts found that of all the participants, 223 had at least one "positive" report for hallucination on their interviews, and 65 received a diagnosis of schizophrenia. The authors said that long-term smokers of marijuana were 4 times more likely to have high scores on a list of psychotic illnesses. Two sample questions included "Do you ever feel as if you are possessed by someone or something else?" and "Do you ever feel as if other people can read your mind?"
In addition, the researchers analyzed the association between marijuana use and psychotic symptoms among a subgroup of 10 pairs of siblings. Within these pairs, not a big difference was noticed in cannabis use. However, among the 218 pairs of siblings where neither had developed a psychotic condition, siblings who had started smoking marijuana at a younger age were more likely to score higher on a questionnaire measuring "delusional-like experiences".
According to the study's lead author, Dr. John McGrath of the Queensland Centre for Mental Health Research, there might be "confounding factors" in this new research. For example, the study did not account for the number of young adults who had psychoses to begin with, and how those conditions could influence their decision to use cannabis. Also, Dr. McGrath added that mental illness among parents "is a potential confounding factor because this could influence both the risk of cannabis use and psychotic-related outcomes in the offspring."
The study will be published in the May issue of the Archives of General Psychiatry, one of the JAMA/Archives journals. The study was funded by the National Health and Medical Research Council of Australia.
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