March 1, 2011

expert reaction to new research on cannabis and psychosis to be published in the BMJ

Research looking at potential link between cannabis use and the risk of psychotic symptoms.

Sir Robin Murray, Professor of Psychiatric Research, Institute of Psychiatry, Kings College London, said:

“This study adds incremental information to the already fairly solid evidence that continued use of cannabis increases risk of psychotic symptoms and psychotic illness. The study is one of ten prospective studies all pointing in this same direction. It adds new information by showing that it is those who show psychotic symptoms within a few years of initiating cannabis use who are especially likely to develop persistent psychotic symptoms if they persist in their use of cannabis.

“In short, this study adds a further brick to the wall of evidence showing that use of traditional cannabis is a contributory cause of psychoses like schizophrenia. However neither this study nor the accompanying editorial address the important question of whether skunk and other potent types of cannabis carry a higher risk of psychosis than traditional resin and marijuana.”

Prof Peter Kinderman, Professor of Clinical Psychology, University of Liverpool, said:

“This is an interesting and potentially important paper by a team of very impressive researchers. It offers more evidence that cannabis use is a risk factor for psychosis and recommends a cautious and thoughtful approach to cannabis legislation.

“Psychosis is common and complex. Psychotic phenomena appear to lie on a continuum – from common but minor quasi-psychotic experiences through to very damaging, life-destroying, problems. And most things that affect human behaviour have been associated with psychotic problems – stress, abuse and traumatic life-events, illnesses and physical health problems, and, in this case, the use of street drugs. A range of risk factors and precipitating factors appear to interact with each individual’s particular vulnerabilities. It’s important to remember that psychosis is a very complex bio-psycho-social phenomenon … but this important paper certainly reminds us that there’s a strong link to the use of cannabis.”

Continued cannabis use and risk of incidence and persistence of psychotic symptoms: 10 year follow-up cohort study, Jim van Os et al, published in the BMJ at 23.30hrs UK time Tuesday 1 March.