STUDY: POT USE BY TEENS LINKED TO PSYCHOSIS

Young adults who used marijuana as teens were more likely to develop
schizophrenia and psychotic symptoms, including hallucinations and
delusions, than those who didn't, an Australian study has found. Those
who used the drug for six or more years were twice as likely to
develop a psychosis such as schizophrenia or to have delusional
disorders than those who never used marijuana, according to research
released online by the Archives of General Psychiatry. They were also
four times as likely to score high on a list of psychotic-like
experiences.

The findings build on previous research and show that marijuana use
isn't as harmless as some people think, lead study author John McGrath
said. The authors said the study was the first to look at sibling
pairs to discount genetic or environmental influence and still find
marijuana linked to later psychosis.

McGrath said his researchers were looking for causes of schizophrenia.
The researchers looked at 3,801 young adults.

Of the 1,272 participants who had never used marijuana, 26, or 2
percent, were diagnosed with psychosis. Of the 322 who had used
marijuana for six or more years, 12, or 3.7 percent, were diagnosed
with the illness. The study showed 65 people overall diagnosed with
psychosis.

Researchers found that those who used marijuana the longest were four
times more likely than those who didn't to have the highest scores
derived from a list of psychotic-like experiences.

Even those who used marijuana for less than three years still had an
increased risk of scoring higher than those who had not, McGrath said.