Young adults are worryingly casual about cannabis. Most of them regard cannabis as a harmless diversion from the monotony of life. It makes them feel relaxed and "chilled" and what can be wrong with that, they ask?
There are now numerous studies linking cannabis to mental illness but so far, campaigners for the legalisation of cannabis say, that none of these prove that cannabis causes mental illnesses such as schizophrenia.
That is partly true but there is a strong possibility that it does, in at least some cases. A study published in the Lancet journal of February 18 suggests that 24pc of first episodes of psychosis may have been caused by cannabis.
Psychosis is a term used to describe a set of symptoms in which the person has lost contact with reality. The condition can be very acute in onset but in others, particularly when multiple acute episodes have been reported, they can rumble beneath the surface causing persistence difficulties in day to day living.
In the acute phase the person is usually distressed or agitated while also suspicious and hostile. Sometimes they "hear others talking about them". These are very frightening experiences and can lead to violence.
The most recent study from King's College Hospital in London with over 606 subjects managed to follow up 76pc of the sample while controlling for factors called confounders, that muddy the waters.
These include age, gender, employment status, other drug use and ethnicity. Dr. Di Forti and her team identified a significant effect of the potency of the cannabis. She found that with high potency the odds of having a first psychotic episode were 1.9 for those using it less than once per week, 2.7 for those using it at weekends only and 5.5 for those using it daily.
There was no association between low potency cannabis (hash) and psychosis. The finding that the risk of psychosis increases with the potency of the cannabis suggests that this is causal.
The two main constituents of cannabis are THC and cannabinol. THC is the ingredient which in experiments has been shown to produce psychotic symptoms such as hallucinations and delusions.
An earlier study by the same authors in 2012 compared the volume of this in skunk and in standard resin (hash) sold in that area of London. The percentages were 12-18pc and 3.4pc respectively.
The authors point out that these are the first studies to demonstrate that the risk of developing psychosis is much greater among frequent users and especially among those who preferentially use skunk with its high concentration of THC. Those using skunk daily have the highest risk of all.
This creates a significant public health problem since skunk has largely displaced cannabis resin on the streets over the past decade, thus increasing the risk of serious mental health problems among those using it.
For those of us working at the coal face of psychiatry, especially in our emergency departments, psychotic episodes are everyday presentations. The role of cannabis in these is three-fold in my experience.
Firstly, it can trigger a drug-induced psychosis. These are brief and short-lived and they generally resolve quickly, sometimes with, sometimes without any specific treatment. This may take a week or longer since cannabis is metabolised slowly in regular users. In first time and occasional users it is metabolised more quickly.
The second scenario is that with an increasing number of brief, cannabis-induced episodes, they resolve more slowly and ultimately the hallucinations and delusions persist long after cannabis has left the body. In this instance the illness has become independent of the trigger and merges, most commonly, with schizophrenia.
Finally those with pre-existing mental illness such as depression, bipolar disorder or schizophrenia may experience a destabilisation of their illness when they use cannabis. In clinical practice this is probably the most common problem arising with cannabis use.
The author and journalist Patrick Cockburn and his son Henry have written about schizophrenia in Henry's Demons: Living with Schizophrenia, a Father and Son's Story. Cockburn believes that cannabis was the underlying trigger to his son's sad drift into mental illness and in it he examines all the research linking the two.
This book has been dubbed by some as "the tobacco moment" analogous to the discovery that cigarette smoking caused lung cancer.
Sir Professor Robin Murray, Professor Emeritus at the Institute of Psychiatry in London and the world's leading expert on schizophrenia has found that the risk of schizophrenia in the general population is 1pc, for ordinary cannabis use 2pc, for regular smokers 4pc and for regular skunk smokers 8pc.
Cries that these studies and this data are alarmist, are ostrich-like. In the interests of mental health we cannot ignore the scientific evidence and the experience of cannabis' victims any longer. Cannabis is dangerous and every parent should know it.