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03/05/2018 Releaf Myths

Cannabis, psychosis and schizophrenia

Cannabis, psychosis and schizophrenia

  1. What is the spectrum of psychotic disorders?

The World Mental Health survey of 2016 estimated that 1 in 13 people may experience a psychotic episode at least once by the age of 75. Psychotic symptoms or incidences make it difficult for a person to, mainly: distinguish between reality and imagined memories, communicate clearly and to experience basic emotions. Ultimately a person experiences a range of hallucinations or delusional thoughts. Whilst schizophrenia is most commonly mentioned and identified by the media, there are different types of psychotic illnesses

  1. What is Schizophrenia?


Schizophrenia is a complex mental illness characterized by a range of psychotic symptoms that fall into three broad categories of positive (ex. Hallucinations, delusion, racing thoughts), negative (ex. flat emotions, struggle to feel pleasure, poor social functioning) and cognitive symptoms (disorganized thoughts, difficulty concentrating, memory loss). The World Health Organization estimates that worldwide there are more than 21 million people affected by the mental disorder and that 1 in 2 people living with schizophrenia does not receive appropriate care. Schizophrenia can cause considerable discomfort and problems at a personal and community level, however, through community level assistance it is treatable and many people recover from the illness.


  1. How is someone diagnosed and what causes schizophrenia?


The first symptoms of schizophrenia normally begin in childhood and early adulthood. Due to the complex nature of the mental disorder specific diagnosis are usually difficult to carry out at an early stage. Furthermore, there is no single test for schizophrenia and it is usually diagnosed following an assessment by a psychiatrist. A psychiatrist might declare that a person suffers from schizophrenia if the person experiences the symptoms for at least 6 months.


The exact causes of schizophrenia are not known, however psychiatrists suggest that it is triggered or aggravated through the combination of physical, genetic, psychological and environmental factors




  1. What is the relationship between Cannabis and Schizophrenia?


Whilst recognizing that a clear cut no or yes answer is not easy to establish, some researchers highlight that it is important to clearly distinguish between transient psychotic symptoms and prolonged mental diseases such as schizophrenia. Whilst the former are mostly linked to the experience produced by the mind altering properties of cannabis and are of short term in nature, the latter involve more enduring and prolonged (over months) psychotic experiences.


Various studies have tried to establish a causational link between cannabis use and psychotic experiences or schizophrenia. The mind altering effects caused by THC are similar to what the academia considers a psychotic episode or mental imbalance, therefore THC has been sometimes associated with psychosis. Academic literature abounds with various studies that propose a biological or chemical explanation of the link between cannabis and schizophrenia, others include third variables such as family, environment, psychological well-being and traumas.


The following is a list of some of the main studies that tried to understand the enduring effects of cannabis:


  • Swedish Army conscripts: 15 year follow up of 45,570 males

Concluded that those who tried cannabis by age 18 were 2.4 times more likely to develop schizophrenia than those who had not

Dr Stanley Zammit, addressed the number of limitations originating from the Swedish study and established that cannabis use and dosage at baseline (taking into consideration also third variables) predicted an increased risk of schizophrenia

  • Netherlands Mental Health Survey and Incidence Study (NEMESIS): population cohort (1997-1999) of 4,045 males and females aged between 18-65 years concluded that psychotic symptoms increase with the dosage and therefore the bigger the dosage the stronger the association.

  • Dunedin Multidisciplinary Health and Development Study: birth cohort in New Zealand identified that adolescent cannabis users with a variant of the gene catechol-O-methyltransferase (COMT) involved in the metabolism of dopamine, were at risk of developing schizophreniform disorder by the age of 26

  • Dr Anton Grech, compared data of psychotic patients from Malta and South London and concluded that in both cases psychotic patients that persisted in the use of cannabis had more positive (but not negative) symptoms and a more continuous illness at follow-up

  • National Psychiatric Morbidity Survey: a sample of non-psychotic and psychotic persons of the British population concluded that cannabis use and dependence is not linked to an increased risk of experiencing psychotic symptoms but is rather the result of other variables (living in a rural area, lack of social support, adverse life events

  • Dr.Shauli Lev-Ra (2016) cross-sectional study of more than 43,000 people, (Toronto) highlighted that dosage and the potency levels of the cannabis strain play a fundamental role when analysing cannabis and mental health.

  • Dr Ana González-Pinto (2009) Cannabis and first-episode psychosis: cannabis user that experience a psychotic episode and refrain from using cannabis experience a quicker recovery than non-cannabis users


  1. What about tobacco?


It is common knoweldge that cannabis, most commonly smoked in joints, is mixed with tobacco. Studies highlight that globally tobacco mixed with cannabis is a more common occurance as opposed to other routes of administration, such as the use of bongs, pipes and vaporizers. It is interesting to note that Europe leads the way when it comes to tobacco, whilst the Americas predominantly use non-tobacco options. Many argue that tobacco is used as an unexpensive filler, others propose that tobacco acts as a ‘cushion’ and dilutes some of the cognitive effects of cannabis. Nonetheless, it is important to highlight that tobacco, more specifically nicotine, is a psychoactive and highly addictive chemical that kills more than 7 million people a year. Whilst only few studies quantify the role of tobacco when analysing cannabis use, it is interesting to note that concurrent use of the two substances might explain increased episodes of dependence, difficulty to stop and psychosis. One recent study found that using ‘pure’ cannabis, resulted in less problematic cannabis use than those using cannabis mixed with tobacco.



  1. What is ‘cannabis psychosis’?

This term has been frequently used by the psychiatric community to describe a short psychotic episode experienced by a heavy cannabis user. However, when the symptoms persisted, the psychiatrists’ assessment continued to focus on cannabis without properly assessing other variables and triggers directly contributing to the mental imbalance. Prof. David Nutt, warns of a new form of stigmatisation of people with mental health issues and people who use cannabis. Prof. Nutt explains that it is counter-productive to blame patients for their mental condition and to directly attribute cannabis use as the only causational element causing mental illness or psychotic episodes. This is never the case and patients should be educated on different variables and triggers.



  1. Where do we stand?

As provided by the numerous past and ongoing studies on the possible link between cannabis and schizophrenia, it is clear that the causational link is not easy to establish and a cautious interpretation of the data collected and results presented is very important. It is surprising that most studies ignore the type and potency of cannabis used by their patients or focus group, and therefore do not quantify THC:CBD ratio or if cannabis is mixed with tobacco. Cannabis is not a homogeneous substance and different cannabis strains and THC:CBD ratio levels represent different mind and body responses. Studies trying to examine the link between cannabis and schizophrenia or psychotic illnesses should never ignore the type of cannabis being used, dosage, the probable mix with tobacco and use of other substances. Furthermore, genetic predisposition and third variables, thus including past and present psychological triggers are pivotal to provide researchers and users with evidence based research and a holistic approach towards cannabis use, its benefits and dangers.  



Whilst every care has been taken to provide the most updated and accurate information, studies on cannabis and schizophrenia are inconclusive and the information might be revised from time to time.


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