According to a new study conducted by the scientists of the University of Queensland in Australia, teenagers who use cannabis or marijuana for more than six years are more likely to have hallucinations or delusions.

Scientists observed 3,081 adults born between 1981 and 1984 and asked them when they reached 21. Around 18% out of the group had been smoking for three years or less, 16% had been smoking for four or five years, and over
14%had smoked for more than six years. 65 of the group were diagnosed as suffering from schizophrenia while 233 had some form of hallucination.

"Compared with those who had never used cannabis, young adults who had six or more years since first use of cannabis was 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", said Dr. John McGrath.

But they notify that the connection between psychosis and cannabis use is by no means simple. The youngsters who had experienced hallucinations in the early period of their life were more prone to have used cannabis longer and often.