There is a warning that the risk of psychosis is increased if cannabis is used as a teenager or young adult.
The link between cannabis and psychosis has been heavily debated, with questions over whether the connection is casual, or if early psychotic experiences lead people to “self-medicate” with the drug.
The latest research comes from data of more than 1,900 people who took part in a study, aged between 14 to 24 at the start.
Researchers re-examined those involved three and eight years later to analyse the connection between cannabis use and psychotic symptoms.
They found that the volunteers who did not use the drug at the start of the study, but went on to start using, had a higher risk of psychotic symptoms later on.
In those who were using cannabis at the start of the study and carried on, there was also an increased risk of psychotic experiences.
The experts, including from Germany, the Netherlands and the Institute of Psychiatry in London, published their findings in the British Medical Journal (BMJ).
They concluded: “Cannabis use is a risk factor for the development of incident psychotic symptoms.
“Continued cannabis use might increase the risk for psychotic disorder by impacting on the persistence of symptoms.”
The experts found no evidence that psychotic symptoms led to later cannabis use.
Sir Robin Murray, professor of psychiatric research at the Institute of Psychiatry, 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.”
- Continued cannabis use and risk of incidence and persistence of psychotic symptoms: 10 year follow-up cohort study. BMJ 2011; Advance publication.
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