Delusions Likely With Long-term Marijuana Use

A recent study has investigated the likelihood of young people who smoke marijuana to experience delusions, hallucinations or other signs of psychosis.  Findings reveal intriguing connections between long-term use of cannabis and episodes of psychosis.

The study was lead by researcher John McGrath, M.D., of the University of Queensland in Brisbane, Australia and followed 3,801 young people up to age 21 who were born between 1981 and 1984.  The youths were questioned about their use of marijuana and asked details about episodes of hallucinations of delusions that might have occurred during use of marijuana.

Terms of use of marijuana varied throughout the study participants: 17.7% reported using pot for three or fewer years, 16.2% reported using it for four to five years and 14.3% reported using it for six or more years.  Of claims of hallucinations or other signs of psychosis, 233 of study participants reported instances of occurrence and 65 were diagnosed as having a “non-affective psychosis.”  Non-affective psychosis, according to Dr. McGrath, is a broad category of mental disorders that includes schizophrenia.  Patients with non-affective psychosis do not display prominent mood elements, as in bipolar disorder or mania.

In explaining the implications of non-affective psychosis, McGrath writes, “Think of depression.  Many of us get mild or moderate depression from time to time but not all of these individuals meet the criteria for full clinical depression.  So, too, for psychosis; some otherwise well people have isolated symptoms, but no disability.”

The research indicates that long-term use of marijuana by young people doubles the likelihood of developing non-affective psychosis.  The study also concluded that youth who used marijuana for six years or longer were four times as likely to experience delusionary experiences.

In an effort to address the issue of genetic predisposition to mental illness in relation to study data, the researchers of the study compared results with a subgroup of 228 siblings.  Their findings indicate no shared genetic or environmental influences that might lead to psychosis.

Overall, researchers were able to find sufficient evidence to link long-term use of cannabis by young people to experiences of hallucinations or delusion.