Does Cannabis Cause Mental Illness?

For years supporters of cannabis have rejected the many studies that link cannabis with psychosis, claiming that research has yet to fully prove a link. I was on a radio programme some years ago and was challenged to provide evidence that cannabis actually ‘causes’ psychosis. Well, of course I couldn’t because ‘causes’ implies that the action of taking cannabis will definitely result in developing psychosis, in the same way that drinking arsenic will definitely end up in death.

It is impossible for any scientist to say that cannabis is a definite cause of psychosis because it depends on the individual’s age, dosage, gender, and genetic makeup.

There are simply too many variables to categorically state that if anyone uses cannabis, they will, for certain, develop psychosis. What the scientists have been trying to do over the decades is to identify whether there is an ‘association’ or ‘link’ between taking cannabis and the development of mental illness, and that is precisely what they have achieved. There is now compelling evidence if teenagers regularly use cannabis, they substantially increase the risk of damaging their brains, which can lead to long term mental health issues, including psychosis and long-term conditions such as schizophrenia.

That is why it is so disingenuous of supporters of cannabis to keep on repeating that cannabis does not cause mental and downplaying the dangers of cannabis. The tobacco industry used similar arguments in the 1950s, dismissing the studies which showed smoking was linked to cancer and blaming pollution and people’s lifestyles. Thankfully we now have the research on the link between cannabis and psychosis, which is now beginning to convince the sceptics.

After decades and hundreds of studies trying to identify a possible link between cannabis and mental illness, we now have the evidence. In 2017 the US National Academy of Medicine, a completely independent organisation and considered one of the foremost research organisations in America, issued a 468-page research paper entitled, ‘The Health Effects of Cannabis and Cannabinoids’.

They concluded:

“Cannabis use is likely to increase the risk of developing schizophrenia and other psychoses; the higher the use and the younger the person is consuming cannabis, the greater the risk”.

More recently in 2019 another major study, ‘Cannabis Use and the Risk of Psychosis and Affective Disorders’ was undertaken by a team which included one of the world’s foremost experts on cannabis and schizophrenia, Sir Robin Murray. This study produced compelling evidence of the link between cannabis and serious mental illness, especially amongst teenagers. The study looked at 13 major studies that had taken place in different countries around the world. Ten of the studies confirmed the link while two showed a similar trend and one was not considered reliable. The study reported that the incidence of schizophrenia in South London had doubled between 1965 and 1999.

A very recent and large Trans-European study has shown an eight-fold variation in the incidences of psychosis across 17 centres; the highest rates were found in London and Amsterdam, cities where young people have been reported to be taking the high potency cannabis. Indeed, in these two centres the use of high potency cannabis accounted for almost one-third and a half, respectively, of all new cases of psychosis.

The report went on to conclude:

Our findings confirm previous evidence of the harmful effect on mental health of daily use of cannabis, especially of high-potency types. Importantly, they indicate for

the first time how cannabis use affects the incidence of psychotic disorder. Therefore, it is of public health importance to acknowledge alongside the potential

medicinal properties of some cannabis constituents the potential adverse effects that are associated with daily cannabis use, especially of high-potency varieties.

The message is now very clear; the stronger strains of cannabis which now populate Western towns and cities can damage the development of young people’s brains and refutes the arguments that cannabis is safe and does not cause severe mental illness.

This blog is an extract from my book ‘Gone To Pot – Cannabis: What Every Parent Needs To Know’.