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What is cannabis?

Cannabis is derived from the cannabis plant (Cannabis sativa). It belongs to the depressant class of drugs. It is the most widely used illicit drug in Australia (AIHW, 2019).

The main active ingredient in cannabis is delta-9-tetrahydrocannabinol, commonly known as THC. This is the part of the plant responsible for most of the psychoactive effects or the ‘high’. There is a wide range of THC potency between cannabis products. Cannabis also contains the non-psychoactive, cannabidiol (CBD).

Cannabis comes in different forms:


  • Marijuana is the dried leaves and flowers (buds) of the cannabis plant – it is the most common form and is usually smoked in a cigarette (joint) or water pipe (bong)
  • Hashish (or hash) is the dried resin from the cannabis plant and can be smoked or added to foods and eaten
  • Hash oil is oil extracted from hashish – it is the most potent form and can be smoked
  • Concentrates are extracts (dabs, wax or shatter) that typically use butane hash oil as a solvent and are often vaporized in small quantities due to high THC content (ADF, 2019)
  • Edibles are foods that contain cannabis, such as hash/dope cookies and cakes – these products can take one to three hours to take effect and it can be difficult to regulate the amount of cannabis consumed
  • Pharmaceutical products or ‘medicinal cannabis’ are forms of cannabis that have been approved by the Therapeutic Goods Administration (TGA) and typically come in the form of oral solutions or capsules that contain carefully controlled concentrations of THC and CBD or hemp oil.

Synthetic cannabinoids

A range of different chemicals that vary substantially in potency and effects are sold as synthetic cannabis. These products are often labelled as cannabis, but exhibit effects more typically associated with psychostimulants. Synthetic cannabinoids are classified as new/novel psychoactive substances (see new/novel psychoactive substances fact sheet).

Medicinal cannabis

Medicinal cannabis is cannabis prescribed to relieve the symptoms of a medical condition, such as epilepsy. These products are pharmaceutical-grade and tightly quality-controlled, with labelled levels of cannabinoids such as THC and CBD. They often come in the form of oral solution or capsules. Recently, legislation has been passed in Australia to facilitate access to medicinal cannabis for certain medical conditions (ADF, 2019).Prescriptions for these products are only available via a registered health practitioner via the TGA Special Access Scheme or Authorised Prescriber Scheme and are assessed on a case-by-case basis..

What are the effects?

The effects of cannabis vary considerably from one person to another and relevant

factors include mood, body weight, previous experience with cannabis and the type being used.

When cannabis is smoked the active ingredient is absorbed directly from the lungs into the blood stream, so the effect is almost immediate. 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 (Quick Guide to Drugs and Alcohol, 2017).

Short term effects

  • Mild euphoria, relaxation and reduced inhibitions
  • Perceptual alterations, including time distortion and intensification of ordinary experiences
  • Feelings of hunger
  • Panic reactions, confusion and feelings of paranoia – mainly reported by naïve users
  • Nausea, headache and reddened eyes
  • Increased heart rate for up to three hours after smoking
  • Dizziness, with impaired balance and coordination (AIHW, 2019)

Long term effects

  • Physical dependence
  • Upper respiratory tract cancers, chronic bronchitis and permanent damage to the airways when smoked
  • Cardiovascular system damage
  • Mental health conditions including depression
  • Poor adolescent psychosocial development (AIHW, 2019)

What are the risks?

Mixing cannabis with other drugs

The effects of taking cannabis with other drugs − including over-the-counter or prescribed medications − can be unpredictable (ADF, 2019).

Using cannabis with other drugs is more dangerous than using cannabis alone. Common combinations include cannabis and tobacco and cannabis and alcohol (Quick Guide to Drugs and Alcohol, 2017).

Toxicity and overdose

There are no documented cases of death due to acute cannabis toxicity however high doses may produce a number of adverse effects including confusion, amnesia, delusions, hallucinations, anxiety and agitation (Darke, Lappin & Farrell, 2019).

Dependence and withdrawal

The existence of cannabis dependence syndrome was a contested issue for the second half of the 20th century. It is now accepted as a real syndrome and formally included in the DSM V. There is considerable demand for treatment for cannabis withdrawal which also suggests its presence. Data suggests that 10 percent of those who use cannabis will develop dependence. 

Reflecting trends in use, dependence is most common among men in their twenties and thirties. Withdrawal symptoms peak between two and three days after quitting but may persist for weeks. Symptoms include:

  • Insomnia
  • Irritability
  • Depression
  • Anxiety
  • Decreased appetite
  • Gastrointestinal disturbances (Darke, Lappin & Farrell, 2019)

Mental health

Whilst definitive causality is difficult to conclude, there are many associated mental health risks with use of cannabis, including:

  • Psychosis

Mild psychotic symptoms may occur and resolve as the drug leaves the body. However, for some this may persist or occur independently of intoxication. There is considerable research to suggest that cannabis use is associated with an increased risk for psychotic symptoms, schizophrenia, and other psychosis spectrum disorders. 

Those showing a pre-existing vulnerability for psychosis, or a family history should be discouraged from using the drug (Darke, Lappin & Farrell, 2019).

  • Suicide, self-harm and other affective disorders

Anxiety and panic symptoms are regularly observed in cannabis use and daily use is associated with an increased risk for suicide attempts, particularly among adolescents. Suicidal thoughts and behaviours are associated with early and frequent use of cannabis.

Rates of cannabis use among individuals diagnosed with bi-polar are higher than in the general population (Darke, Lappin & Farrell, 2019).

How many people use cannabis?

According to the Australian Institute of Health and Welfare, cannabis continues to have the highest reported prevalence of lifetime and recent consumption among the general population, compared with other illicit drugs (AIHW, 2019). In 2018 11.8% of people aged 18 and over in Australia reported using cannabis in the past 12 months (AIHW, 2020).


Treatment for cannabis dependence and withdrawal is generally administered in an outpatient setting, with supervision from a health professional. Cognitive behavioural therapy focused on improving an individual’s coping skills to prevent relapse has been shown to be effective.

Motivational enhancement and contingency management may also be useful. There are no proven pharmacotherapies for cannabis dependence.

Emergency info

If you, or someone around you, is experiencing undesired or distressing psychological or physical symptoms from the intake of alcohol or other drugs please seek immediate medical attention.

If you need urgent help from ambulance services call Triple Zero (000). If a person has been mixing drugs with alcohol or other drugs, tell the paramedic exactly what has been taken.


For free and confidential advice about alcohol and other drugs, call the National Alcohol and Other Drug hotline on 1800 250 015.

The hotline will automatically direct you to the Alcohol and Drug Information Service in your state or territory.

More resources

The Illicit Drug Reporting System is an Australian monitoring system that identifies emerging trends of local and national interest in illicit drug markets.

The Ecstasy and Related Drugs Reporting System is an Australian monitoring system for ecstasy and related drugs that identifies emerging trends of local and national interest.

The Clinician’s Guide to Illicit Drugs and Health examines the health effects of each of the major illicit drugs.

The Australian Institute of Health and Welfare collects information on alcohol and tobacco consumption, and illicit drug use among the general population in Australia.

The Australian Bureau of Statistics is Australia’s national statistical agency, providing official statistics on a range of economic, social, population and environmental matters of importance to Australia.


A Quick Guide to Drugs and Alcohol (3rd ed.) (2017). Sydney, Australia: Drug Info.

Alcohol and Drug Foundation (2019). Cannabis. Retrieved from https://adf.org.au/drug-facts/cannabis/

Australian Institute of Health and Welfare (2019). Effects of Cannabis [Table]. Retrieved from https://www.aihw.gov.au/reports/alcohol/alcohol-tobacco-other-drugs-australia/contents/drug-types/cannabis

Australian Institute of Health and Welfare (2020). Alcohol, tobacco & other drugs in Australia - Cannabis. Web report: 11 Sept 2020. Retrieved from: https://www.aihw.gov.au/reports/alcohol/alcohol-tobacco-other-drugs-australia/contents/drug-types/cannabis#consumption

Darke, S., Lappin, J., & Farrell, M. (2019). The Clinician’s Guide to Illicit Drugs and Health, Great Britain: Silverback Publishing.