Teenage cannabis use linked to psychosis

Teenagers and young adults using cannabis are at a greater risk of psychosis later in life, a study has found.

Although many studies have linked cannabis use to psychosis, it has not been clear whether the drug causes symptoms such as hallucinations and confusion, or is used by people to help relieve pre-existing mental illness.

In this study, a team of international researchers led by Professor Jim van Os from Maastricht University looked at cannabis use and the development of psychotic symptoms in more than 1,900 young people aged between 14 to 24, over 10 years.

The researchers excluded anyone who reported cannabis use or pre-existing psychotic symptoms at the beginning of the study. The remaining participants were then assessed for cannabis use and psychotic symptoms at three time points during the study.

The study found that cannabis use almost doubled the risk of psychotic symptoms later in life, and continued use of cannabis during the study period increased the risk of persistent psychotic symptoms.

This was true even after taking into account other factors such as age, sex, socio-economic status, use of other drugs, and other psychiatric conditions.

Sir Robin Murray, professor of psychiatric research at the Institute of Psychiatry at King's College, London, said the research was one of 10 prospective studies which all pointed in the same direction, suggesting that cannabis use is a "contributory cause of psychoses like schizophrenia."

The study findings are published online in the British Medical Journal.

This article was published on Wed 2 March 2011