Study linking psychosis to high-potency cannabis based on guesswork


A study claiming to link high-potency cannabis to psychosis was based on guessing the strength of the THC based on the name of the strain they had used. (Don’t laugh!)

Qualifying the findings, the authors of the study admitted that it was limited by small numbers of participants at each site; that THC and CBD content of the cannabis was not directly measured; and that the results might, at least in part, be down to those at greater risk of psychosis being more likely to use cannabis. Fancy that – people with psychosis might turn to cannabis for relief from it.

It may or may not make things better in individual cases but people are willing to give it a try. Certainly, as we have said before, cannabis can risk amplifying existing mental health issues, because it heightens lucidity. But studies undertaken with this in mind are far and few between.

This didn’t stop the ‘progressive’ Guardian reporting the findings as fact in its headline without so much as a quotation mark.

This kind of research is not helping anyone apart from prohibitionists. Much deeper research into cannabis is required. Research like this continues to assume negative aspects of cannabis use and are therefore not objective.

The study estimated that 30% of first-time cases (60 per year) of psychotic disorders in south London, and half of those in Amsterdam, could be avoided if high-potency cannabis was not available.

The study, led by Dr Marta Di Forti from King’s College London, collected between mid 2010 and mid 2015 for 901 adults under the age of 65 who arrived at mental health services in one of 10 locations in Europe, or one in Brazil, and received their first diagnosis of a psychotic disorder that was not down to, for example, brain tumours or acute drug use.

For comparison, the team asked more than 1,200 healthy individuals from across the same areas about their cannabis use. The strength of cannabis was estimated from the name individuals gave to the drug. But were the other polluting ingredients that usually come with street cannabis considered? Apparently not.

After taking into account factors including drinking, education and use of other drugs such as ketamine, the team found those with a psychotic disorder were more likely to have used cannabis “at some point in their life” than those without the condition.

Frequency of use was also highlighted by researchers: the chances of having a psychotic disorder were 40% greater among those who used the drug more than once a week compared with those who rarely, if ever, used it, while the chances of having a psychotic disorder were more than three times greater among those who used cannabis daily compared with those who rarely if ever used it.

Daily users of high potency cannabis were more likely to have a psychotic disorder, compared with never-users, than those who used low-potency cannabis every day.

The Guardian notes that Di Forti admitted “that not all daily users of high-potency cannabis develop a psychotic disorder, meaning it is important to work out who is most vulnerable, and that other factors are also at play.”

Other, wider-ranginf studies, have found that THC, the psychoactive cannabinoid, is more therapeutic than CBD.

Last month, Ian Hamilton, a researcher in psychology at University of York, told us the problems with the current forms of research into cannabis.

Regarding this new study, he told Popular Science: “I think sometimes it’s useful to zoom out a little bit. We’ve known about this association for a long time,” which leads him to question what this new research adds to the picture.

He said the risk of psychosis as a result of marijuana consumption is just one in 20,000.

And he said that, in the UK, mixing tobacco and cannabis in joints and become addicted to nicotine as a result is a much bigger concern.

Rather than trying to add more levels of detail into the picture of how cannabis use is linked to psychosis, he says, “I think what would be far more interesting [and] far more useful is to try and work out who has a problem before they’re exposed to cannabis.” That way, people at high risk of developing psychosis could be identified and reached by targeted public health interventions.