Last updated: August 2013
Cannabis, or marijuana, is the most commonly used illegal drug. It comes from the Cannabis sativa plant. It can be smoked or eaten, and comes in a variety of forms, such as dried plant leaves and flowers (‘heads’), a crumbly, light-brown or dark-brown resinous material called ‘hash’, or a very potent oil called ‘hash oil’.
The chemical in cannabis that makes users feel ‘high’ is called THC (delta-9 tetrahydrocannabinol). THC is a psychoactive substance, which means that it travels in a person’s bloodstream to the brain. It disrupts their brain’s normal functioning and causes certain intoxicating effects.
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 not use cannabis.
Types of cannabis
There are several forms of cannabis, including:
- marijuana – the most common and least concentrated form. It is made from dried plant leaves and flowers. The flowers, or ‘heads’, are the most potent forms of the plant. Marijuana looks like chopped grass and ranges in colour from grey-green to greenish-brown. It is usually smoked in a water pipe (bong), pipe or hand-rolled cigarette (joint).
- hashish – small blocks of dried cannabis resin. Blocks range in colour from light brown to nearly black. The concentration of THC in hashish is higher than in marijuana
- hash oil – a thick, oily liquid extracted from hashish, ranging in colour from golden-brown to black. It is usually spread on the tip or paper of cigarettes and then smoked. Hash oil is more potent than the other forms of cannabis.
Synthetic cannabis
In recent years, a wide range of synthetic products, claiming to have similar effects to cannabis, have also been available in Australia. Synthetic cannabis is made up of chemicals that are designed to activate the same chemical systems in the brain as THC. These drugs are marketed as having similar physical and psychological effects as cannabis, but can have more unpredictable effects and are potentially more harmful than cannabis.
Medicinal cannabis
Medicinal cannabis refers to approved, quality assured cannabis products prescribed by your doctor and taken to treat the symptoms of a medical condition or the side effects of treatment. Read more about medicinal cannabis.
Effects of cannabis use
Cannabis is a depressant drug. Depressant drugs do not necessarily make you feel depressed. Rather, they slow down your central nervous system and the messages going between your brain and your body.
Cannabis has different effects on different people. The effect can also vary according to the mood or atmosphere in which the person uses it. The immediate effects of cannabis can last approximately two to three hours and may include:
- a feeling of relaxation and wellbeing
- loss of inhibition
- reduced concentration and memory
- distorted perceptions of time, space and distance
- increased heart rate
- drowsiness
- increased appetite
- increased talkativeness
- reddened eyes
- reduced coordination – this makes it dangerous to drive or operate machinery while under the influence of the drug
- anxiety and paranoia.
Larger doses or stronger forms of cannabis can increase these effects, and can also cause:
- confusion
- restlessness
- feelings of excitement
- hallucinations
- anxiety or panic
- detachment from reality
- nausea
- psychosis (severe mental illness where the person loses connection with external reality).
Cannabis and psychosis
Research suggests that cannabis use can make a person’s existing psychotic symptoms worse. It may even bring on psychotic symptoms in people who are predisposed to psychosis if they have a personal or family history of psychosis.
Cannabis use can cause a condition known as drug-induced psychosis. Symptoms usually appear quickly and last a few days until the effects of the cannabis wear off. Disorientation, memory problems and hallucinations (seeing or hearing things that are not really there) are the most common symptoms.
Cannabis and 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 and more intense.
Cannabis and 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.
When people experience psychotic symptoms, they are unable to distinguish what is real. They lose contact with reality.
Worsening of psychotic symptoms through cannabis use
Cannabis use generally makes psychotic symptoms worse and lowers the person’s 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 for them. People with a psychotic illness should not use cannabis.
