BBC News 2 March 2011
Using cannabis as a teenager or young adult increases the risk of psychosis, a report suggests. The study published in the British Medical Journal involved tracking 1,900 people over a period of 10 years. Although the link between cannabis and psychosis is well-established, it had been unclear whether cannabis triggers the disorder. This research strongly suggests that cannabis use comes first, rather than people taking it for their symptoms. The research was led by Professor Jim van Os from Maastricht University in the Netherlands, and included researchers from the Netherlands, Germany, Switzerland and the UK. They excluded anyone who reported cannabis use or pre-existing psychotic symptoms at the start of the study, which took place in Germany. The participants in the study, aged between 14 and 24, were assessed for cannabis use and psychotic symptoms at three points over a 10-year period. It found that cannabis use “significantly” increased the risk of psychotic symptoms, even when other factors such as socio-economic status, use of different drugs and other psychiatric conditions were taken into account.