Mental health and substance use Print this page

Key points

This page provides a short summary on mental illness and psychological distress as they relate to substance use. For more detailed information and data, refer to Alcohol, tobacco & other drugs in Australia: People with mental health conditions. This page also provides information on comorbidity between mental illness and substance use disorders, which themselves are classified as mental illness.

What is the relationship between mental illness and substance use?

The relationship between mental illness and substance use is complex (for the relationship with substance use disorders, see section below). A mental illness may make a person more likely to use drugs as an attempt to self-medicate symptoms associated with their mental illness. Conversely, substance use may be a contributing factor for the initial symptoms of mental illness. Certain substances may cause a substance-induced psychosis which can last for days or weeks after the end of intoxication. There is evidence that individuals who experience substance-induced psychosis are at significant risk of later transitioning to long-term psychotic illness (Vassos 2023). Critically, this does not mean that substance use necessarily triggers mental illness or vice versa: common risk factors (such as trauma, personality traits, genetic influences and the childhood environment) may cause substance use and mental illness to independently develop in the same individual (UNODC 2022).

The 2022–2023 National Drug Strategy Household Survey (NDSHS) (Figure SU.1) found that, compared with adults without a mental illness, those with a mental illness were:

• more likely to drink alcohol at risky levels (37% compared with 32%)
• twice as likely to smoke daily (15% compared with 7.4%) 
• 1.8 times as likely to use any illicit drug (29% compared with 16%).

For further information and data, refer to the National Drug Strategy Household Survey 2022–2023: Mental health and use of alcohol, tobacco, e-cigarettes and other drugs.

A recent study of Australian general practice records (Belcher et al. 2021) showed the rate of moderate to heavy drinking among patients with severe mental illness and/or long-term mental illness was 4.7%, more than double that for the population without (2.2%). The same study also showed almost half (47%) of people with severe or long-term mental illness are current or past smokers, compared with almost one third (30%) of the population without (Belcher et al. 2021).

The 2010 National Survey of High Impact Psychosis (SHIP) showed rates of smoking, harmful use and dependence of alcohol and illicit drugs among adults living with psychotic illness were well above the general population. Among those living with psychotic illness, 66% reported currently smoking compared with 25% of the general population. Half of people living with psychotic illness (51%) had a lifetime history of harmful alcohol use or dependence, double the rate in the general population (25%), and over half (55%) had a lifetime history of harmful illicit drug use or dependence – 6 times the rate of the general population (9%) (Morgan et al. 2012).

Psychological distress and substance use

Psychological distress describes acute mental stress which is caused by life circumstances or mental illness (Tian et al. 2021), though not all people who experience psychological distress necessarily have a diagnosable mental illness. It may include nervousness, agitation, psychological fatigue, depression and anxiety. Psychological distress has a similar relationship to substance use as mental illness – psychological distress can lead to substance use (Moe et al. 2024) and substance use can lead to psychological distress (Booth et al. 2010).

The 2022–2023 NDSHS found that, compared with adults experiencing low levels of psychological distress, those experiencing high or very high levels of psychological distress were:

• more likely to drink alcohol at risky levels (39% compared with 30%)
• 2.3 times as likely to smoke daily (15% compared with 6.7%)
• 4.1 times as likely to use vape or use e-cigarettes (16% compared with 3.9%)
• 2.5 times as likely to use any illicit drug (32% compared with 13%).

For further information and data on the relationship between psychological distress and substance use, refer to the National Drug Strategy Household Survey 2022–2023: Mental health and use of alcohol, tobacco, e-cigarettes and other drugs.

Comorbidity of substance use disorders with other mental illnesses

Substance use disorders – which are categorised as a type of mental illness  – are the third most prevalent category of mental disorder among Australian adults, with an estimated 650,000 (3%) Australian adults experiencing substance use disorders in the 12 months prior to the 2020–2022 National Study of Mental Health and Wellbeing (ABS 2023).

Comorbidity between substance use disorders and other mental illnesses is common (Mills et al. 2019). According to the NSMHW 2020–2022, while 9% of people who met the diagnostic criteria for an anxiety disorder or affective disorder also met the criteria for a substance use disorder, 46% who met the diagnostic criteria for substance use disorder, also met the criteria for an anxiety or affective disorder (ABS 2023). Among people entering alcohol and other drug treatment programs in Australia, between 50–76% meet the diagnostic criteria for at least one comorbid mental illness (see Mills et al. 2019).

Comorbidity of substance use disorders and other mental illnesses increases the already heavy burden a person would experience with either of these in isolation (Leung et al. 2016). Compared to people with no comorbidity, people with comorbid substance use disorder and mental illness are more likely to experience poorer short- and long-term outcomes for their mental health and substance use, levels of impairment that are more severe, and greater use of health services (Leung et al 2016).

While mental illness is associated with a reduced life expectancy (Lawrence et al. 2013), research has shown that the combination of substance use disorder with another mental illness is associated with markedly higher mortality rates and larger reductions in life expectancy (Plana-Ripoll et al 2020). This aligns with the relatively high fatal disease burden associated with substance use disorders compared to most other types of mental illness. While the 2023 Australian Burden of Disease Study does not contain data on comorbidity of substance use disorders and other mental illness, Mental and substance use disorders were estimated to be responsible for 15% of the total burden of disease, placing it second as a broad disease group after Cancer (17%) (AIHW 2023).

Where can I find more information?

For more information, refer to:

• Alcohol, tobacco and other drugs in Australia: People with mental health conditions
• National Drug Strategy Household Survey 2022–2023: Mental health and use of alcohol, tobacco, e–cigarettes and other drugs
• Physical health of people with mental illness
• National Study of Mental Health and Wellbeing, 2020–2022
• Australian Burden of Disease Study 2023

Data in this section were last updated in July 2024.