Can Marijuana Cause Psychosis?

Cannabis & psychosis

Can Marijuana Cause Psychosis?

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 schizophrenia.

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.

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 ly to experience psychosis, but your genetics, early development and life experiences have a much stronger effect on your chances of becoming ill.

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 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 ly 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 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.

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.

This SANE factsheet is currently being reviewed by industry professionals and people with lived experience.


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.


Does cannabis cause mental illness?

Can Marijuana Cause Psychosis?

Cannabis is the most commonly used illicit drug in Australia, with one in three adults using it at some point in their life. It’s legal in some places around the world, and offered medicinally in others. But what does smoking pot do to your mental health?

The potential harms associated with using cannabis depend on two things above all others.

The first is the age at which you first begin to use cannabis, particularly if it’s before 18. Using cannabis during key stages of brain development can impact on synaptic pruning (when old neural connections are deleted) and the development of white matter (which transmits signals in the brain).

The second is the patterns of use: the frequency, dose and duration, particularly if you’re using at least weekly. The bigger or more potent the dose, the more tetrahydrocannabinol (THC) you are ingesting. THC is the main psychoactive component of cannabis and appears to act on areas of our brain involved in the regulation of our emotional experiences.

Depression and anxiety

Many studies of the relationship between cannabis use and mental illnesses such as depression and anxiety have suffered from methodological issues by not controlling for related factors.

The few longitudinal studies that have been conducted have mixed findings.

A 2014 review of the existing research concluded that using cannabis placed an individual at moderate risk of developing depression.

Unfortunately it was not within the scope of the research to determine if cannabis use wascausing depression or if the relationship instead reflects the association between cannabis use and social problems. Cannabis use is associated with other factors that increase risk of depression such as school dropout and unemployment.

The relationship between cannabis use and anxiety is also complex. Many people use cannabis for its euphoric and relaxing effects. But some people also experience feelings of anxiety or paranoia when intoxicated. As such, cannabis could be used to relieve anxiety or stress for some while causing others to feel anxious.

A 2014 review of the available research concluded that using cannabis placed an individual at a small risk of developing anxiety. But the authors noted that while the weight of evidence supported the coexistence of cannabis use and anxiety, there was relatively little evidence to suggest that cannabis caused anxiety.

Not included in these previous reviews of depression and anxiety disorders were two recent investigations of cannabis use in the United States using data from 2001-2002 and 2004-2005. These included a host of variables such as demographic status and family environment.

Each found a significant association between cannabis use and the onset of depression and anxiety disorders. But this association was no longer significant when considering the impact of the included variables.

Clearly, the relationship between cannabis use and depression and anxiety disorders is complex and involves the individual’s reasons for cannabis use and external situations. That is, cannabis may be used to help cope with social problems that were not necessarily caused by cannabis use.


In contrast, the relationship between cannabis use and risk of developing symptoms of psychosis has been well established in many different review articles.

This research has found that early and frequent cannabis use is a component cause of psychosis, which interacts with other risk factors such as family history of psychosis, history of childhood abuse and expression of the COMT and AKT1 genes. These interactions make it difficult to determine the exact role of cannabis use in causing psychosis that may not have otherwise occurred.

Regardless, the connection between cannabis use and psychosis is not surprising.

There is a strong resemblance between the acute and transient effects of cannabis use and symptoms of psychosis, including impaired memory, cognition and processing of external stimuli.

This combines to make it hard for a person to learn and remember new things but can also extend to the experience of deluded thinking and hallucinations.

We also know that cannabis use by people with established psychotic disorder can exacerbate symptoms.

Overall, the evidence suggests cannabis use will bring forward diagnosis of psychosis by an average of 2.7 years.

The risk of developing schizophrenia increases with the duration and dose of cannabis use. Regular cannabis users have double the risk of non-users. Those who have used cannabis at some point in their life have a 40% increased risk compared with non-users.

That said, it is important to view this increased risk in context. The proportions of individuals with psychosis among the population and among cannabis users are low. Current estimates suggest that if frequent long-term cannabis use was known to cause psychosis, the rates of incidence would increase from seven in 1,000 in non-users to 14 in 1,000 cannabis users.

If you or a family member or friend have problems or concerns about cannabis, visit or access the free national Cannabis Information and Helpline on 1800 30 40 50.

This article was first published in The Conversation. Click here to read the original article.


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