The most common physical health effect of long-term cannabis use is an increased risk of respiratory diseases associated with smoking (including cancer). This risk has been shown to be present even in the absence of tobacco smoke, while harms appear to be additive for individuals who smoke both tobacco and cannabis. Cannabis use is additionally associated with a range of mental health problems that may also increase risk to physical health.

Also see FAQ: What are the health risks of cannabis use?

Australians (aged 18 years and older) who used cannabis in the past 12 months are more likely to have been diagnosed with or treated for a mental illness in the past year, compared to those who did not use cannabis (27% vs. 15%).

There were 6,100 hospital separations due to cannabis use disorders in 2018-19.

Men accounted for more hospital separations due to cannabis use disorders than women in 2018-19.

Australians aged 20-29 years accounted for the largest proportion of hospital separations due to cannabis use disorders in 2018-19 (44%).

Two types of cannabis use disorders resulted in hospital separations in 2018-19.  These were ‘mental and behavioural disorders due to the use of cannabinoids’ (accounting for 5,686 or 93% of separations), and ‘poisoning by cannabis’ (accounting for 414 or 7% of separations).

Cannabis use has been linked to a range of mental health conditions including:

• panic attacks
• depression and anxiety
• psychotic episodes
• schizophrenia
• dependence.

Not everyone who uses cannabis develops mental health problems. However, for some people, cannabis can contribute to the development of mental health symptoms or make an existing mental health condition worse. Cannabis-related mental health problems can arise at any stage of cannabis use.

While uncommon, heavy cannabis use can result in short-term drug-induced psychosis. However, psychotic symptoms usually cease when cannabis use is stopped. There is also some evidence that cannabis use may trigger schizophrenia in those who are already at risk of developing the disorder. Cannabis use can double the risk of schizophrenia in those who are vulnerable, and bring on a first episode earlier. Heavy cannabis use and using cannabis at a young age are associated with up to six times greater risk for schizophrenia; especially using three or more times per week before the age of fifteen.

The link between cannabis and other more common mental health disorders such as depression and anxiety is unclear, as cannabis is often used to relieve the symptoms of these conditions. However, people who use cannabis have been shown to have higher levels of depression and more depressive symptoms than those who do not use cannabis. There is growing evidence to suggest that cannabis use, particularly frequent or heavy use, predicts depression later in life. Young women appear to be more likely to experience this effect.

See also FAQ: What are the health risks of cannabis use?

A larger proportion of Australians (aged 18 years or older) who used cannabis in the past 12 months reported high or very high levels of psychological distress (16% and 12%, respectively) compared to those who did not use cannabis in the past 12 months (8% and 4%, respectively).

The reference guide used by clinicians to diagnose mental health disorders is known as the Diagnostic and Statistical Manual of Mental Disorders (DSM). The most recent version of the manual, the Diagnostic and Statistical Manual of Mental Disorders – 5th Edition (DSM-5), was released in May 2013. Prior to this, the Diagnostic and Statistical Manual of Mental Disorders – 4th Edition, Text Revision (DSM-IV-TR) was used by clinicians and researchers from 2000 to 2013.

The diagnostic criteria for mental health disorders due to cannabis use differ significantly between the DSM-IV-TR and the new DSM-5. These differences are explained in more detail below. For the purposes of the NADK, all reported data on cannabis-related mental health disorders utilise the DSM-IV-TR diagnostic criteria. This is because the relevant mental health data reported in the NADK was collected prior to the publication of the newer version of the DSM (DSM-5).

DSM-IV-TR Diagnostic Criteria

According to the DSM-IV-TR, there are two main mental health disorders caused by cannabis use: cannabis dependence and cannabis abuse. The diagnostic criteria for each are presented below.

Cannabis Dependence

Cannabis dependence is defined by the DSM-IV-TR as:

A maladaptive pattern of cannabis use, leading to clinically significant impairment or distress, as manifested by at least three of the following occurring at any time in the same 12-month period:

1. Tolerance, as defined by either of the following:

a.   A need for markedly increased amounts of the substance to achieve intoxication or desired effect.

b.   Markedly diminished effect with continued use of the same amount of the substance.

2. Withdrawal, as manifested by either of the following:

a.   The characteristic withdrawal syndrome for cannabis.

b.   Cannabis, or a cannabis-like substance, is taken to relieve or avoid withdrawal symptoms.

3. Cannabis is often taken in larger amounts or over a longer period than was intended.

4. A persistent desire or unsuccessful efforts to cut down or control cannabis use.

5. A great deal of time is spent in activities necessary to obtain cannabis, use cannabis, or recover from its effects.

6. Important social, occupational, or recreational activities are given up or reduced because of cannabis use.

7. Cannabis use is continued despite knowledge of having a persistent or recurrent physical or psychological problem that is likely to have been caused or exacerbated by cannabis.

Cannabis Abuse:

Cannabis abuse is defined by the DSM-IV-TR as:

A.  A maladaptive pattern of substance use leading to clinically significant impairment or distress, as manifested by at least one of the following, occurring within a 12-month period:

1. Recurrent cannabis use resulting in a failure to fulfil major role obligations at work, school, or home.
2. Recurrent cannabis use in situations in which it is physically hazardous.
3. Recurrent cannabis-related legal problems.
4. Continued cannabis use despite having persistent or recurrent social or interpersonal problems caused or exacerbated by the effects of cannabis.

B. The symptoms have never met the criteria for Cannabis Dependence.

DSM-5 Diagnostic Criteria

According to the DSM-5, there is one main mental health disorder caused by cannabis use: cannabis use disorder.

Cannabis Use Disorder

Cannabis use disorder is defined by the DSM-5 as:

A problematic pattern of cannabis use leading to clinically significant impairment or distress, as manifested by at least two of the following, occurring within a 12-month period:

1. Cannabis is often taken in larger amounts or over a longer period than was intended.
2. There is a persistent desire or unsuccessful efforts to cut down or control cannabis use.
3. A great deal of time is spent in activities necessary to obtain cannabis, use cannabis, or recover from its effects.
4. Craving, or a strong desire or urge to use cannabis.
5. Recurrent cannabis use resulting in a failure to fulfil major role obligations at work, school, or home.
6. Continued cannabis use despite having persistent or recurrent social or interpersonal problems caused or exacerbated by the effects of cannabis.
7. Important social, occupational, or recreational activities are given up or reduced because of cannabis use.
8. Recurrent cannabis use in situations in which it is physically hazardous.
9. Cannabis use is continued despite knowledge of having a persistent or recurrent physical or psychological problem that is likely to have been caused or exacerbated by cannabis.
10. Tolerance, as defined by either of the following:

a.   A need for markedly increased amounts of cannabis to achieve intoxication or desired effect.

b.   A markedly diminished effect with continued use of the same amount of cannabis.

   11. Withdrawal, as manifested by either of the following:

a.   The characteristic withdrawal syndrome for cannabis (refer to DSM-5 for further details).

b.   Cannabis (or a closely related substance) is taken to relieve or avoid withdrawal symptoms.

 A mild cannabis use disorder is defined as the presence of 2-3 of the above symptoms.

A moderate cannabis use disorder is defined as the presence of 4-5 of the above symptoms.

A severe cannabis use disorder is defined as the presence of 6 or more of the above symptoms.