What is cannabis?

Cannabis comes from the plant Cannabis sativa. The main active ingredient in cannabis is delta-9-tetrahydrocannabinol (D9THC). It is D9THC that gives users the ‘high’.

The drug comes in 3 main forms:

  • marijuana — the dried leaves or flowers (heads) of the plant;
  • hashish (or ‘hash’) — dried blocks of cannabis resin; and
  • hash oil — extracted from hashish.

Marijuana is usually smoked in hand-rolled cigarettes (joints) or in a water pipe (bong). Hashish can also be smoked or added to food and eaten (e.g. ‘hash cookies’).

How common is cannabis use?

Cannabis is the most commonly used illegal drug in Australia. In the 2010 National Drug Strategy Household Survey, about one-third of the population reported having used cannabis at some time in their lives.

Effects of cannabis

Acute intoxication

The effects of acute intoxication with cannabis (being ‘stoned’ or ‘high’) may include:

  • a sense of wellbeing;
  • feeling relaxed and drowsy;
  • impairment of memory, concentration and problem solving;
  • loss of co-ordination;
  • dry mouth and red eyes; and
  • an increase in heart rate.

With higher doses of the drug there may also be:

  • altered perceptions (for example, of time and space);
  • panic and anxiety;
  • confusion; and
  • paranoia and hallucinations.


Heavy cannabis use may cause an acute toxic psychosis (a mental state in which a person loses contact with reality). Also, in people who already have schizophrenia, cannabis use can cause their psychotic symptoms to worsen.

Physical health

Because cannabis users often also smoke tobacco, it is difficult to separate the effects of cannabis on physical health from the effects of tobacco. Possible long-term effects of cannabis use may include increased risk of chest infections, chronic bronchitis and cancers of the lungs, head and neck. Chronic cannabis use can also affect fertility in men and women.


About one in 10 users will become dependent on cannabis. Many regular users find it hard to stop using cannabis, even though they may want to.

Treatments for cannabis dependence

For those cannabis users who do become dependent, treatment with cognitive behavioural therapy — a type of psychological therapy also known as CBT — may help them to cut down on their use.

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