Mar 24, 2011

Marijuana use during adolescence and young adulthood increases the risk of psychotic symptoms, while continued cannabis use may increase the risk for psychotic disorder in later life, concludes a new study published in the British Medical Journal.

Cannabis is the most commonly used illicit drug in the world, particularly among adolescents, and is consistently linked with an increased risk for mental illness. However, it is hasn’t been clear whether the link between cannabis and psychosis is causal, or whether it is because people with psychosis use cannabis to “self- medicate” their symptoms.

So a team of researchers, led by Professor Jim van Os from Maastricht University in the Netherlands, investigated the association between cannabis use and the incidence and persistence of psychotic symptoms over 10 years.

The study occurred in Germany and involved a random sample of 1,923 teens and young adults from the ages of 14 to 24.

Incident cannabis use almost doubled the risk of later incident psychotic symptoms, even after accounting for factors such as age, sex, socioeconomic status, use of other drugs, and other psychiatric diagnoses. Furthermore, in those with cannabis use at the start of the study, continued use of cannabis over the study period increased the risk of persistent psychotic symptoms. There was no evidence for self medication effects as psychotic symptoms did not predict later cannabis use.

These results “help to clarify the temporal association between cannabis use and psychotic experiences,” the authors said in their study summary. “In addition, cannabis use was confirmed as an environmental risk factor impacting on the risk of persistence of psychotic experiences.”

Source: British Medical Journal March 2011