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Cannabis comes from the Cannabis sativa plant. It acts as a central nervous system depressant that also alters sensory perceptions.

cannabis buds

The primary active ingredient is THC (delta-9 tetrahydrocannabinol), which is responsible for the mood-altering effects of cannabis, the ‘high’ and the unpleasant mental health effects, such as paranoia, experienced by users. However, it also contains numerous other cannabinoids, chemicals produced by the plant, which play a number of roles that are still being discovered.  One of the most important of these is cannabidiol (CBD), which has important potential medicinal effects, and may help counteract some of the unpleasant effects of THC on mental health.  Worldwide research has shown a shift towards the cultivation of cannabis with high levels of THC and low levels of CBD over the past decade or more.

Cannabis comes in different forms. The most common are:

  • marijuana, the dried leaves and flowers of the cannabis plant  —this is the weakest form
  • hashish (or hash), the dried resin from the cannabis plant, which is stronger than marijuana
  • hashish oil (or hash oil), which is oil extracted from hashish, which is the most potent form

It can also come in the form of edibles and increasingly, highly concentrated extracts, such as wax and cannabinoid oils.

The cannabis plant has been used for centuries for very different purposes:

  • its effects as a drug
  • as a medicine
  • the production of hemp fibre.

Cannabis was first used for medical and religious purposes in China, India and the Middle East. It was introduced to the Western world via India in the early 1800s, and was the most commonly used drug for pain relief before the introduction of aspirin in the late 1800s. 

Cannabis and the law

The use, possession and supply of cannabis is illegal in all states and territories in Australia. It is also illegal to possess items used to take cannabis, such as bongs. In NSW, first offenders with a small amount of cannabis may be issued with a formal caution, which can include information about the harm associated with cannabis use and a number to call for drug-related information or referral. A person can receive up to two cautions. 

More serious or subsequent offences may lead to a period of imprisonment.

The medicinal use of cannabis

The medicinal use of cannabis has become increasingly common, as a number of states in the USA and several countries in Europe and South America have legalised possession and use for this purpose. In some places the crude cannabis plant is permitted to be used, while there are also some registered pharmaceutical preparations developed from the plant, which typically contain THC and/or CBD, e.g., nabiximols, (Sativex). 

There is evidence that cannabis preparations may be useful for treating spasticity in multiple sclerosis patients, withdrawal symptoms in people addicted to cannabis and some forms of pain. In some cases, side effects seemed to outweigh benefits and more research is required to confirm how effective it is compared to existing medicines. 

People with a terminal illness may be eligible to legally use cannabis to alleviate their symptoms, under the Medicinal Cannabis Compassionate Use Scheme

Medicinal cannabis is currently not readily available in Australia, although use may be granted in exceptional circumstances. For example, the NSW Medicinal Cannabis Compassionate Use Scheme, aims to assist police in exercising discretion towards registered users (aged 18 years and older), and their carers, who may use cannabis products to help alleviate symptoms. Trials on the efficacy of cannabis for certain medical conditions are also currently underway in NSW. 

For more information go to Centre for Medicinal Cannabis Research and Innovation  

How cannabis is used

Marijuana is most commonly smoked, rolled up in a cigarette paper (a joint) or in a water pipe (a bong) — usually, but not necessarily, with tobacco. The use of vaporisers (‘vaping’), which heat cannabis products without combustion, has increased as people have become concerned about the effects of smoking cannabis. ‘Dabbing’, which is the inhalation of vapours from concentrated forms of cannabis extracts using solvents, is also becoming more common. 

The plant material can also be cooked into food and eaten. 

Cannabis statistics

Cannabis is the most commonly used illegal drug in Australia. The 2022-23 National Drug Strategy Household Survey (NDSHS) reported an increase in people reporting having used cannabis at some point in their lifetime. 2 in 5 people (41%) had used cannabis at some point in their lifetime, the highest proportion seen since data collection began in 2001 and an increase from the 37% in the 2019 survey.

In 2022–‍2023, 11.5% of people in Australia had used cannabis in the previous 12 months, equating to around 2.5 million people. This was similar to 2019, when 11.6% of people had done so, but is still lower than the proportion doing so in 2001 (12.9%).


Short term effects

When cannabis is smoked the active ingredient is absorbed directly from the lungs into the blood stream, and then on to the brain and other organs, so the effect is almost immediate. Cannabis acts on specific receptors in the brain. 

Cannabis eaten in food takes longer to have an effect (up to 60 minutes), as it must be digested before it can enter the blood stream. Oral absorption is highly variable so the effects are unpredictable. This method does not carry the risks associated with smoking, but the time lapse between consumption and effect makes it hard for the user to judge how much to take.

The effects of cannabis vary considerably from one person to another. Relevant factors include mood, body weight, the person’s previous experience with cannabis and the type being used. In some cases there may be no noticeable effects at all.

Short-term effects may include:

  • a feeling of being ‘stoned’—relaxed, euphoric and uninhibited
  • enhanced sensory perceptions, particularly enjoying food, for example,  or music
  • feelings of hunger (having ‘the munchies’)
  • panic reactions, confusion and feelings of paranoia
  • nausea, headaches and reddened eyes
  • increased heart rate for up to three hours after smoking
  • dizziness, with impaired balance and coordination.

Cannabis intoxication can impair a person’s ability to perform tasks requiring coordination, judgement and quick reactions, such as driving.

The short-term effects of cannabis can last from two to four hours, but the drug is stored in fatty tissue and slowly released back into the bloodstream before being excreted from the body. Traces of cannabis can be found in urine for one to five days after occasional use and up to six weeks (or more) in people who use cannabis regularly (more than three times a week, over a number of years). While cannabis can be detected in many bodily fluids (eg, blood, urine and saliva) and hair, it is difficult to assess the meaning of a positive result.

Due to the lengthy storage of cannabis in the system, positive test results may indicate recent use rather than impairment. This is particularly important when considering random driver and workplace testing for cannabis. 

Long term effects

Ongoing heavy use may increase the risk of:

  • developing cannabis dependence
  • upper respiratory tract cancers, chronic bronchitis and permanent damage to the airways when smoked (particularly when smoked with tobacco)
  • cardiovascular system damage (the heart and circulation)
  • experiencing negative mental health effects.

Babies whose mothers smoke cannabis in pregnancy are more likely to be born prematurely and have a low birth weight, probably mainly due to the fact that they smoke tobacco. 

Cannabinoid hyperemesis syndrome 

Associated with long-term chronic cannabis use, cannabis ‘hyperemesis’ (severe vomiting) is a rare syndrome characterised by recurrent nausea, vomiting and stomach pain. Hot baths may be helpful in relieving symptoms temporarily, and symptoms stop when cannabis use is ceased. The exact mechanisms responsible for causing the symptoms are unknown.

Cannabis and driving

It is dangerous and illegal to drive under the influence of cannabis. Research suggests that a driver affected by cannabis is two to three times more likely to have an accident. 

Random drug testing of drivers for cannabis (an ‘oral fluid’ test) has been introduced in NSW. 

Cannabis and pregnancy

If a pregnant woman smokes cannabis with tobacco—the most common way of using cannabis—the unborn baby is exposed to the risks presented by tobacco smoking. Cannabis-smoking in pregnancy also increases the risk that the baby will be born prematurely. 

Cannabis also passes into breast milk, which means that it is likely to affect a breast-fed baby. 

Parents who smoke cannabis, especially with tobacco, in the presence of children risk exposing them to the dangers of passive smoking. This increases the risk of SIDS (sudden infant death syndrome), bronchiolitis and childhood asthma. 

Cannabis and mental health

Cannabis use can have serious consequences for the mental health of particularly vulnerable people. It increases the frequency of episodes of psychosis in those with a disorder such as schizophrenia. Whether it can cause a psychotic illness is not known, but it appears that heavy use at a young age can bring about a psychotic episode in susceptible individuals, and at a younger age. The association between anxiety and depression is less certain, but there is some evidence that regular, long term cannabis use from an early age may increase the risk of experiencing symptoms into adulthood. Regular adolescent use may also increase the risk of attempting suicide. 

Using cannabis with other drugs

Cannabis is often used with other drugs. 

Using cannabis with any other drugs (illegal or prescription) is more dangerous than using cannabis alone. Cannabis and tobacco are a common combination. The risks to the respiratory and cardiovascular systems of using both drugs appear to be higher than for using either cannabis or tobacco alone. 

It is also common to mix alcohol and cannabis, and there is evidence that  even small doses of the two drugs together can impair driving performance  to a greater extent than either alone. 


Regular users of cannabis can become dependent. 


Symptoms of cannabis withdrawal tend to be similar to those of tobacco withdrawal. They include increased anxiety, mood swings, sleep problems, aggression, reduced appetite and cravings for cannabis. While individual symptoms may be milder than those of drugs such as alcohol and heroin, in combination they can still contribute to a relapse to use. Symptoms tend to peak two to three days after quitting but may last for several weeks. 


Treatment for cannabis dependence and withdrawal is generally on an outpatient basis under supervision from a health professional. Cognitive behavioural therapy, focused on improving the person’s coping skills to prevent relapse, has been found to be effective. Motivational enhancement and contingency management may also be useful. There  are currently no proven pharmacotherapies available to treat those with  a cannabis problem. 

Is cannabis a gateway to hard drugs? 

There has been ongoing debate about whether cannabis acts as a ’gateway’ to the use of other illegal drugs such as heroin or speed. It is true that many people who take these drugs previously used cannabis. However, the majority of people who try cannabis do not go on to use cannabis regularly,  or to use other illegal drugs.

People who consider cannabis a gateway drug argue that the cannabis affects the body and mind in a way that makes an individual more susceptible to other drug use. However, there may be other reasons for an association; for example, the person may have a tendency to engage in risky behaviour, which leads to experimentation with a variety of drugs. 

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