Daily Cannabis Use May Up Risk for Developing Psychotic Disorder

People who smoke cannabis on a regular basis are much more likely to experience delusions, severe depression and other symptoms of psychosis - with the risk increasing significantly with more potent forms of the drug, a new study finds.

Cannabis is defined as being strong when it has a THC level of more than 10 per cent.

If high-THC cannabis - including strains such as "trainwreck", "gorilla glue", and "hindu kush" - were no longer available, "12 per cent of cases of first-episode psychosis could be prevented across Europe", the researchers calculated. They they also predict that first-time psychosis cases in Amsterdam would fall from 38 to 19 per 100,000 annually, and in London from 46 to 32 per 100,000. They analyzed these participants' history of cannabis use. The high potency cannabis is called skunk in the UK. The scientists also classified the potency of the cannabis consumed as either "high" (over 10 per cent THC) or "low" (under 10 per cent THC).

A new study published Tuesday in the Lancet Psychiatry journal shows people who use cannabis every day or those who use high-potency weed are at increased risk of psychotic disorder.

Several past studies have found that more frequent use of pot is associated with a higher risk of psychosis - that is, when someone loses touch with reality. All of the subjects were diagnosed with first episode psychosis and observations were compared with a control group from the local populations. Corresponding rates in London were 21.0% for daily use, and 30.3% for high potency use.

Many countries have legally approved cannabis use.

Di Forti notes that their observations do not show that psychosis is a direct result of using cannabis; however, she warns this research should be taken into consideration, especially by mental health physicians.

Even the Royal College of Psychiatrists is reviewing its position to consider the view that decriminalisation would give the government power to regulate its strength and generate taxes.

"The use of cannabis with a high concentration of THC has more harmful effects on mental health than the use of weaker forms", said lead author Marta Di Forti, a professor at the Institute of Psychiatry, Psychology and Neuroscience at King´s College London. It is perfectly possible that the association between cannabis and psychosis is bidirectional. "Given the changing legal status of cannabis across the world, and the associated potential for an increase in use, the next priority is to identify which individuals are at risk from daily potent cannabis use, and to develop educational strategies and interventions to mitigate this".

Experts analyzed data from 11 sites across Europe and Brazil. It was paid for by funders including Britain's Medical Research Council, the Sao Paulo Research Foundation and the Wellcome Trust.

For the first time it also looked at 900 psychosis patients and...