What is cannabis?

Cannabis refers to the products of the cannabis sativa plant, also known as marijuana and hashish (depending on which part of the plant is used). Cannabis is widely available for use as a recreational drug. It is commonly taken by mixing with tobacco and smoking as a hand-rolled joint, or by inhaling through a water-cooled pipe called a bong. It may also be cooked in food and eaten.

How many people use cannabis?

Cannabis is the most widely used illicit drug in Australia. Around 30 per cent of the population have tried cannabis at some time. Among people under 35 years of age, about 50 per cent had tried it at some time, and 28 per cent had used it in the past year.

How does cannabis affect the brain?

Cannabis contains a chemical known as tetrahydrocannabiol (THC). THC is a psychoactive substance. This means it travels through the bloodstream to the brain, disrupting its usual functioning and causing certain intoxicating effects. Some of these effects can be pleasant at the time; some are unpleasant. Most of these effects are short-term; some can be long-term.

What are the effects of cannabis?

Common effects include a feeling of relaxation; loss of inhibition; increased talkativeness; confused perception of space and time; sedation; and reduced ability to concentrate and remember. Other effects may include paranoia, confusion and increased anxiety. With heavy use there may also be hallucinations.

How long do the effects last?

The effects begin within minutes and can last for up to several hours. For people with a psychotic illness, or who have a predisposition to such an illness, the effects can be more serious and long-term. Psychotic illnesses are characterised by symptoms such as delusions, hallucinations and thought disorder. When people experience psychotic symptoms, they are unable to distinguish what is real — there is a loss of contact with reality.

Does cannabis cause psychotic illnesses such as schizophrenia?

Use of cannabis can cause a condition called drug-induced psychosis. This usually passes after a few days. However, if someone has a predisposition to a psychotic illness such as schizophrenia, these drugs may trigger the first episode of an ongoing condition such as schizophrenia. There is increasing evidence that regular cannabis use precedes and even causes higher rates of psychotic illness. At the same time, many people with schizophrenia have not used cannabis.

How does cannabis affect someone with a psychotic illness?

Cannabis generally makes psychotic symptoms worse and lowers the chances of recovery from a psychotic episode. People with a psychotic illness, such as schizophrenia, who use it experience more hallucinations, delusions and other symptoms; they have a higher rate of hospitalisation for psychosis, and treatment is generally less effective and recovery more difficult.

So should someone with a psychotic illness avoid drugs such as cannabis?

Yes. The consequences can be so serious for the person's health that it is best to avoid drugs such as cannabis completely. People at higher risk of developing a psychotic illness – if they have other family members with the illness, for example – should also avoid using cannabis. It can be helpful to look at other, healthier ways of relaxing and socialising as an alternative.

Last Reviewed: 01/01/2012

Reproduced with the kind permission of SANE Australia.


1. sane Australia. 2012. Cannabis and psychotic illness. http://www.sane.org/images/stories/information/factsheets/1211_info_fs4cannabis.pdf (accessed Feb 2013.)