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Cannabis use can cause drug-induced psychosis, trigger the first episode of a psychotic illness, or make a pre-existing psychotic illness worse. Cannabis comes in three forms - as either marijuana, hashish or hash oil. People who have, or may be at risk of developing, a psychotic illness should avoid using cannabis.
Cannabis is the most widely used illicit drug. It is derived from the Cannabis sativa plant and comes in three forms: marijuana, hashish and hash oil. The chemicals in cannabis interfere with normal brain functioning. Cannabis use can cause drug-induced psychosis, trigger the first episode of a psychotic illness or make a pre-existing psychotic illness worse. People who have, or may be at risk of developing, a psychotic illness should avoid using cannabis.
Cannabis is a psychoactive drug
Cannabis contains a chemical commonly known as THC (delta-9 tetrahydrocannabinol). THC is a psychoactive substance, which means that it travels in the bloodstream to the brain. It disrupts usual brain functioning and causes certain intoxicating effects, including:
- A feeling of relaxation and wellbeing
- Loss of inhibition
- Increased talkativeness
- A confused perception of space and time
- Reduced ability to concentrate and remember
- Reduced coordination – this makes it dangerous to drive or operate machinery while under the influence of the drug.
Heavy use may cause hallucinations
Other possible effects, which are more common with heavy cannabis use, include:
- Paranoia
- Confusion
- Anxiety.
Drug-induced psychosis
Cannabis use can cause a condition known as drug-induced psychosis. Symptoms usually appear quickly and last a relatively short time (a few days) until the effects of the cannabis wear off. Disorientation, memory problems and visual hallucinations are the most common symptoms.
People who already have a psychotic illness may experience longer lasting and more intense symptoms.
Cannabis effects last longer if you have a psychotic illness
The effects of cannabis begin within minutes and can last several hours. However, for people with a psychotic illness (such as schizophrenia), the effects can be longer lasting.
Cannabis can precipitate the first episode of psychosis
If someone has a predisposition to a psychotic illness, such as schizophrenia, use of drugs such as cannabis may trigger the first episode in what can be a lifelong, disabling condition. There is increasing evidence that regular cannabis use precedes and causes higher rates of psychotic illness. Psychotic illnesses are characterised by:
- Delusions – for example, the person believes they have special powers.
- Hallucinations – for example, the person hears voices or sees things that aren’t really there.
- Thought disorder – for example, the person has difficulty organising their thoughts.
Psychotic symptoms can become worse
Cannabis use generally makes psychotic symptoms worse and lowers the chances of recovery from a psychotic episode. People with a psychotic illness who use drugs experience more delusions, hallucinations and other symptoms. They have a higher rate of hospitalisation for psychosis, and treatment is generally less effective. People with a psychotic illness should avoid using cannabis.
Where to get help
- SANE Helpline. Tel. 1800 18 SANE (7263)
- Your doctor
- Family Drug Help – for information and support for people concerned about a relative or friend using drugs Tel. 1300 660 068
Things to remember
- THC (a chemical found in cannabis) interrupts normal functioning of the brain.
- Cannabis use can cause drug-induced psychosis, leading to symptoms such as visual hallucinations.
- Cannabis use can worsen symptoms associated with psychotic illnesses (for example, delusions and hallucinations).
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Fact sheet currently being reviewed.
Last reviewed: September 2011
Content on this website is provided for education and information purposes only. Information about a therapy, service, product or treatment does not imply endorsement and is not intended to replace advice from your doctor or other registered health professional. Content has been prepared for Victorian residents and wider Australian audiences, and was accurate at the time of publication. Readers should note that, over time, currency and completeness of the information may change. All users are urged to always seek advice from a registered health care professional for diagnosis and answers to their medical questions.
Cannabis use can cause drug-induced psychosis, trigger the first episode of a psychotic illness, or make a pre-existing psychotic illness worse. Cannabis comes in three forms - as either marijuana, hashish or hash oil. People who have, or may be at risk of developing, a psychotic illness should avoid using cannabis.
Content on this website is provided for education and information purposes only. Information about a therapy, service, product or treatment does not imply endorsement and is not intended to replace advice from your qualified health professional. Content has been prepared for Victorian residence and wider Australian audiences, and was accurate at the time of publication. Readers should note that over time currency and completeness of the information may change. All users are urged to always seek advice from a qualified health care professional for diagnosis and answers to their medical questions.
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