Australian Study Shows Possible Link Between Marijuana and Psychosis

Australian mental health researchers have possibly found a link between marijuana use and psychosis. According to a Yahoo News report (via HealthDay.com):

Australian researchers asked nearly 3,100 young adults averaging about 20 years of age about marijuana use. They found that almost 18 percent reported using the drug for three or fewer years, about 16 percent for four to five years, and just over 14 percent for six or more years.

Among the participants, 65 had been diagnosed with a "non-affective psychosis" such as schizophrenia, and 233 had at least one positive item for hallucination on a diagnostic interview conducted for the study.

"Compared with those who had never used cannabis, young adults who had six or more years since first use of cannabis [i.e., who commenced use when around 15 years or younger] 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]," wrote Dr. John McGrath, of the Queensland Centre for Mental Health Research, Park Centre for Mental Health in Wacol, and colleagues. "There was a 'dose-response' relationship between the variables of interest: the longer the duration since the first cannabis use, the higher the risk of psychosis-related outcomes."

The researchers also found a connection between hallucinations and marijuana, but the link is unclear. Many of the people who experienced hallucinations began doing so at a young age, and they also commenced using marijuana at an early age. The researchers beleive that marijuana could have enhanced a predisposition in the individuals for hallucinations.