Life Health & Wellbeing

Wednesday 26 June 2019

Study proves cannabis can lead to psychosis

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Stock Photo

Patricia Casey

Last year, a small study of 96 young cannabis users (aged 16 to 21) in Ballymun, north Dublin cast a disturbing spotlight on their financial circumstances. It found that, on average, each user spent about €108 per week on the drug. An extension of the study examined those youths who were unemployed and not in a training programme. Their spend amounted to €152 each week, or almost €8,000 per year.

How this was compatible with survival is unclear as most, according to the report, would have been on jobseekers' allowance, amounting to around €100 per week. There was also a growing attrition rate from training programmes compared to earlier years. Debt, low motivation and finance-driven crime are all considerations that those working with young cannabis users are trying to deal with.

A 2016 study by Peter Barrett and Colin Bradley from UCC Medical School and published in the Irish Journal of Medical Science examined Cork students aged between 15 and 18. Just under 40pc of these secondary school students reported cannabis use at some point in their lives. Those who perceived it to be mentally and physically dangerous were less likely to abuse it. This is hardly surprising.

There is now good evidence that cannabis is dangerous, but advocates of cannabis still question this. They claim that pre-existing severe psychiatric illness may, in many cases, have driven these young people to use cannabis to alleviate their symptoms, rather than cannabis being the cause. Now most studies take account of this possibility either by excluding those with symptoms of schizophrenia or by controlling for the severity of these at the index interview and factoring this into the statistical analysis.

The latest study to examine the question of whether cannabis use in adolescence increases the risk of schizophrenia later in life was published in the April issue of the British Journal of Psychiatry. This Northern Finland study was headed by Dr Antti Mustonen from Oulu University, examining over 6,500 babies born in 1986.

Their first interview was conducted when they were aged 15 to 16 and those who were psychotic by then were excluded. Information was obtained on cannabis and other substances, both legal and illicit, as well as alcohol, using a questionnaire. They were screened for early symptoms of schizophrenia, referred to as prodromal symptoms.

This information was linked to a national register for schizophrenia when the group reached the age of 30. The severity of prodromal symptoms when present, as well as details of any family history and misuse of other substances, was controlled in their complex statistical analysis.

The findings are stark. Adolescent cannabis use increased the risk of psychosis by the age of 30, even after adjusting for severity of prodromal symptoms, parental psychosis and other substance use. The risk applied in those who had used cannabis five times or more by the time they were 15 to 16.

Furthermore, those who had prodromal symptoms and used cannabis had double the risk of full-blown psychotic symptoms compared to those with prodromal symptoms and not using cannabis. These findings are striking since this is one of the largest studies of its kind.

This study adds to the list of investigations examining this question. The first study on the relationship between cannabis and psychosis was published in 1987, while one of the best designed, known as the Dunedin study from New Zealand, was published in 2000. The number has grown since and all point to an association between cannabis and psychosis.

The current concerns are a long way from the heady days of 1998 when thousands gathered in Hyde Park London to call for the decriminalisation of cannabis. Among them were Paul McCartney, the late Anita Ruddock (of Body Shop fame) and Rosie Boycott, then-editor of the British Independent, who spearheaded it. They were joined by writers such as Nick Hornby, Martin Amis and Harold Pinter. Less than 10 years later, Boycott published an apology for having misguided the British public about cannabis, saying "if only we had known then what we can reveal today".

What they had come to realise was that the cannabis of the good old days was much less potent than the now widely-available 'skunk'. Cannabis has two main constituents, THC and cannabinol, and it is THC which produces the psychotic symptoms of hallucinations and delusions. It is the concentration of this which has increased in skunk. It is likely just a matter of time before science will conclusively show that it does indeed cause major mental illness. Anybody concerned about this should read the article, available online, called 'My son played Russian Roulette with cannabis - and lost' by Patrick Cockburn and his son Henry Cockburn.

Meanwhile many a young lives, like Henry's, continue to be blighted, either because of denial or ignorance.

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