Illicit cannabis use can result in a range of adverse physical and mental health outcomes. Long-term use of cannabis can result in impairments to cognitive functioning, including memory and attention. In general, more prologued use results in greater impairment – people who use cannabis for many years may not recover full cognitive function even when they stop using.

Inhaling cannabis smoke can also lead to respiratory problems such as bronchitis, airway injury and lung inflammation, and may increase risk of lung, throat, and oral cancer. In pregnant women, cannabis use is associated with impaired fetal development and reduced birth weight.

There is a strong association between cannabis use and psychosis or psychotic disorders such as schizophrenia. Among people with a genetic predisposition, cannabis use may trigger psychosis or make existing symptoms worse. Other mental health conditions are also associated with cannabis use, including depression and suicidal thoughts and behaviours.

There were 6,503 hospital separations due to cannabis use disorders in 2022-23.

Men accounted for more hospital separations due to cannabis use disorders than women in 2022-23.

Australians aged 20-29 years accounted for the largest proportion of hospital separations due to cannabis use disorders in 2022-23 (40%).

Two types of cannabis use disorders resulted in hospital separations in 2022-23.  These were ‘mental and behavioural disorders due to the use of cannabinoids’ (accounting for 6,117 or 94% of separations), and ‘poisoning by cannabis’ (accounting for 386 or 6% of separations).

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 is the Diagnostic and Statistical Manual of Mental Disorders – 5th Edition (DSM-5).

DSM-5 Diagnostic Criteria for 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.

Australians (aged 18 years and older) who used cannabis in the past 12 months are significantly 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 (30% vs. 16%).

A significantly 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 (19% and 12%, respectively) compared to those who did not use cannabis in the past 12 months (10% and 5%, respectively).