What is cannabis?
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.
- 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.
- 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.
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.
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.
Last Reviewed: 12/05/2017
1. SANE Australia. Content last reviewed: 12 May 2017 Cannabis and psychosis. https://www.sane.org/information-stories/facts-and-guides/cannabis-and-psychotic-illness (accessed Nov 2019.)
Cannabis can affect your physical and mental health with heavy cannabis use potentially causing psychosis.
Cannabis/marijuana: what are the effects?
The effect of cannabis on a person depends on many factors including their size, weight and health and the amount taken.
Do cigarettes increase the risk of psychosis?
We know that smoking increases the risk of most chronic diseases and substantially shortens lifespan, but can it effect our mental health?
When someone experiences psychosis they are unable to distinguish what is real. Symptoms include confused thinking, delusions and hallucinations.
Schizophrenia is a serious mental illness which affects about one person in 100 in Australia. Experts divide the symptoms into positive and negative symptoms.