Quick Facts
Cannabis (marijuana, hashish, weed, dope) is the most commonly used illicit recreational drug in Australia. It’s a depressant psychoactive substance that can cause temporary psychotic symptoms and, in some cases, full psychotic disorders like schizophrenia.
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Cannabis facts
- It’s addictive: cannabis contains THC, a highly addictive chemical.
- It’s common: more than 1 in 10 Australians aged 14+ have used cannabis in the past year
- It’s very common in people with psychotic disorders: cannabis use is much higher in people living with psychotic disorders than in the general population or even people with other mental illnesses. Up to a quarter of people diagnosed with schizophrenia may also have a cannabis use disorder.
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Cannabis myths
- Myth: ‘A little bit is harmless’
- Reality: Cannabis can cause psychotic symptoms even at low doses.
- Myth: ‘My mate is fine, so I’ll be fine’
- Reality: Cannabis affects different people differently. Other people’s use can’t predict your reaction.
- Myth: ‘Cannabis is the biggest cause of psychosis’
- Reality: Cannabis use makes you more likely to experience psychosis, but your genetics, early development and life experiences have a much stronger effect on your chances of becoming ill.
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Can cannabis cause psychosis?
Here’s what research says about cannabis use and psychosis:
Cannabis use can cause you to experience psychotic symptoms
Along with the traditional high, cannabis use can cause paranoia, delusions and hallucinations in people who don’t already have a mental illness, even in small doses.
Cannabis use can also trigger or worsen psychotic symptoms in people living with an illness like schizophrenia, even when their illness is otherwise stable and responding well to treatment.
Cannabis can trigger a psychotic illness in susceptible people
Some things can make it more likely that you will experience a psychotic disorder at some point in your life. These include your genetic make-up, your mother’s health during pregnancy, complications with your birth, child abuse, some kinds of head injury and infection, drug abuse, living in urban areas and experiencing high stress and social disadvantage.
If you already have a predisposition like this, cannabis use can trigger an illness. It can also cause symptoms to occur far sooner than they would otherwise have done.
Although anyone can experience psychotic symptoms from cannabis use, it hasn’t been demonstrated yet whether cannabis can cause a psychotic illness in someone who isn’t otherwise susceptible.
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What about medical marijuana?
Medical marijuana was made legal in Australia in late 2016. It has a growing range of uses, but it isn’t a proven treatment for psychotic illness.
If you’re worried about the risk of psychosis in using medical marijuana to treat another condition, talk to your doctor.
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References
Schoeler T, Monk A, Sami MB, et al. ‘Continued versus discontinued cannabis use in patients with psychosis: a systematic review and meta-analysis.’ Lancet Psychiatry. 2016;3(3):215-225.
Johanna Koskinen, Johanna Löhönen, Hannu Koponen, Matti Isohanni, Jouko Miettunen; Rate of Cannabis Use Disorders in Clinical Samples of Patients With Schizophrenia: A Meta-analysis. Schizophr Bull 2010; 36 (6): 1115-1130. doi: 10.1093/schbul/sbp031
Nunez, L. and M. Gurpegui, ‘Cannabis-induced psychosis: A cross-sectional comparison with acute schizophrenia.’ Acta Psychiatrica Scandinavica, 2002. 105: p. 173–178.
Favrat, B., et al., ‘Two cases of “cannabis acute psychosis” following the administration of oral cannabis.’ BMC Psychiatry, 2005. 5(17)
D’Souza, D.C., et al., ‘Delta-9-tetrahydrocannabinol effects in schizophrenia: Implications for cognition, psychosis, and addiction’. Biological Psychiatry, 2005. 57: p. 594–608.
Dean K and Murray RM (2005) ‘Environmental risk factors for psychosis’. Dialogues Clin Neurosci. 7(1): 69-80.
Veen, N.D., et al., ‘Cannabis use and age at onset of schizophrenia.’ American Journal of Psychiatry, 2004. 161: p. 501–506.
McLaren J, Lemon J, Robins L and Mattick RP, Cannabis and mental health: put into context. Commonwealth of Australia, 2008, p.33.
