February 2013


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DECRIMINALIZATION: With global discussions about the impact of decriminalization of the use of marijuana ongoing, UWI TODAY, sought expert analysis on the milieu.

There continues to be considerable debate about the addictive potential of cannabis and its role as a gateway drug to more dangerous and problematic drug use. Heavy users of cannabis are likely to be less productive than their non-using counterparts apart from, perhaps, the creative industries where quality might be prized more than quantity. There is however a significant risk that early initiation of regular use, as in puberty and early adolescence, does impair one’s capacity for optimal brain function, and therefore is going to result in a diminished productive potential.

While the direction of the relationship remains unclear, it is quite accepted that some cannabis users are more likely to also drink alcohol, smoke cigarettes and even abuse prescription drugs. It has also been suggested that its chronic use may also raise the risk of developing smoking related conditions, such as cancer and obstructive lung disease. There is evidence to indicate that university students are more likely to use cannabis if they have never used before, or increase their use if they have. This may be due to increased independence and peer pressure but many who start during this period do not continue in the same pattern once they complete formal tertiary education.

This suggests that cannabis, as with other drugs, can be used relatively harmlessly, apart from its illegality, but that there are some people whose use of it creates problematic substance use and/or mental health problems. Cannabis use has been found to be associated with a greater need for social relationships and pleasurable experience and as an additional or sometimes sole coping strategy.

This is best illustrated in the one area where consensus has been achieved with regard to the risk of cannabis use. This is its relationship to the development of psychotic illness and schizophrenia. A history of cannabis use is perhaps the single greatest predictor of young men being admitted to the St Ann’s Psychiatric Hospital with psychotic symptoms (hallucinations, strange beliefs and strange speech or behaviour usually occurring over at least a two-week period with an accompanying decrease in normal role functioning). These symptoms mean that people so affected lose the ability to engage with reality in an effective and consistent way, leading to inappropriate social behaviour and the need to seek help. A specific syndrome of hyper-religiosity, aggression and decreased self care has been thought to characterise this union of cannabis use and psychosis. Early work has also linked its use with bipolar disorder, which was labelled as marijuana modified mania.

As much as twelve percent of cannabis users will have at least one psychotic episode in the aftermath of its use, although some of these will not be severe enough to warrant any mental health intervention. The evidence is now quite consistent that early use (early adolescence), prolonged and heavy use and use of more potent varieties, increase the risk of developing a psychotic illness by as much as eight times that of someone who does not engage in use in any of the above categories.

It does appear that those on the pathway to psychosis experience a cumulative toxic effect of cannabis that is manifested about 7-8 years after initiation of use. Users of cannabis have an earlier age of onset of psychotic illness than those who do not use, again suggesting some toxic impact on the brain of vulnerable individuals. It may be that those who will develop psychosis are also more likely to smoke cannabis and abuse other substances, but the relationship between cannabis and psychosis proneness is now beyond doubt.

The relationship is therefore definitely complex but there is accumulating genetic evidence to support the proposition that the negative impact of cannabis on serious mental illness is significantly more likely to occur in those who have vulnerable or psychosis prone genes. Whether it is an actual cause of this illness or acts to facilitate the manifestation of the condition in someone already genetically vulnerable, it does seem that heavy use of the potent variety does generate risk independent of any predisposition genetic or otherwise. Continued use is associated with worse short and long term outcomes and may also negatively affect cognition until use is discontinued. Many research studies in Australia, Europe and the United States have confirmed these associations so much so that prevention of cannabis use has emerged as one of the genuine public health strategies to decrease the incidence and prevalence of psychotic illness.

In one intriguing study, the association between cannabis use and adult psychosis was mediated by childhood sexual trauma. The researchers found that the combination of childhood trauma and cannabis use far more strongly predicted adult psychosis than either risk factor alone. Other mediating factors proposed include urban living, male gender and being exposed to chronic stress in early development.

Another interesting finding is that people with attention deficit hyperactivity Disorder (ADHD) are more likely to use cannabis than their peers without the disorder. This is likely to be a form of self medication and suggests that drug use that becomes problematic may in fact reflect underlying pathology that requires treatment. Cannabis use seems to increase, or at least the cravings increase, when the user experiences negative affective states as in feels depressed or is struggling to cope with life’s issues. This is similar to the findings of an association between alcohol abuse and dependence and depression and other mood disorders. A bidirectional relationship between cannabis use disorders and major depression has been reported with greater levels of depression seen in those who are afflicted by both cannabis and alcohol use disorders.

This association with other negative health behaviours also includes an increased risk of self harm and suicide. A report from India last year described an individual who engaged in the act of self amputation of his genitalia as a consequence of his paranoid symptoms occurring in the aftermath of cannabis use.

Frequent recreational use in adolescence is also associated with an increased risk for depression and anxiety disorders in young adult women, a finding that is unlikely to be due to self medication according to the researchers, as girls with depression and anxiety are no more likely to use cannabis than others. Again the issue of cause and effect needs to be clarified. What is clear is that those who develop serious illness are more adversely affected if they continue to use cannabis. There is a greater loss of brain volume and functional outcomes tend to be worse, including more frequent hospitalisations.

The impact on cognition leads to a greater frequency of accidents including road traffic accidents and poorer academic performance in the medium to long term, this even in people without psychosis.

Smoking cannabis therefore does confer a risk on some of the people who smoke it to develop serious mental illness, however the majority of people who smoke it will have no problems, but how will you tell the difference and if you want to start, is it worth the risk?

Gerard Hutchinson is a Professor of Psychiatry and Head of the Psychiatry Unit of the Faculty of Medical Sciences, UWI.