1 What are concurrent disorders? 

Mental illnesses are conditions in which people’s thinking, mood and behaviours may negatively affect their day-to-day functioning. Mental illnesses can affect people of any age, but they often appear in teenage years or early adulthood. 

There are several types of mental illnesses. Mental health problems can include depression, anxiety, schizophrenia and many other disorders, as well as addictions (Public Health Agency of Canada, 2015a). They can range from single, short-lived episodes to chronic disorders (Public Health Agency of Canada, 2015b). 

Addiction occurs along a continuum from mild to moderate to severe. In the extreme, it can be characterized by the four Cs: craving, loss of control of the amount or frequency of use, compulsion to use and use despite negative consequences. 

A person with a mental health problem has a higher risk of having an addiction problem, just as a person with an addiction problem has an increased chance of having a mental health problem. When someone is diagnosed with both mental health and addiction dis.orders, they are said to have concurrent disorders. 

Concurrent disorders can include combinations such as: 

• an anxiety disorder and problematic alcohol use 
• schizophrenia and cannabis use disorder 
• borderline personality disorder and substance use disorder 
• depression and addiction to sleeping pills. 

Many other combinations are possible, because there are many types of mental health and addictive disorders. It should also be noted that people with concurrent disorders may have more than one addictive disorder and more than one mental health disorder. It is therefore important to view concurrent disorders as involving multiple factors rather than just two disorders, and that these factors are often intertwined. 
  

How common are concurrent disorders?

A 2020 national survey on concurrent disorders among adults aged 18 or older in the United States found that in the past year: 

• 14.2 per cent (or 35.9 million people) had mental illness only 
• 8.3 per cent (or 20.9 million people) had a substance use disorder only 
• 6.7 per cent (or 17.0 million people) had both mental illness and a substance use disorder (SAMHSA, 2021). 

People with substance use disorders are more likely to also have mental health problems than those without substance use disorders (Chan et al., 2008; Harris & Edlund, 2005). About three quarters of people with addictive disorders have pre-existing mental health issues (Rush et al., 2010). The risk of having concurrent disorders increases with the number of substances used (Cooper & Calderwood, 2004). 

In 2012, an estimated 6.1 per cent of the Canadian household population aged 15 to 64 had a mood/anxiety disorder in the previous year and 3.8 per cent had a substance use disorder.  An additional 1.2 per cent experienced concurrent mood/anxiety and substance use disorders (Khan, 2017).

The following sections show the prevalence of mental health and substance use disorders.
  

Anxiety disorders

• In 2012, almost 9 per cent of Canadians met the criteria for generalized anxiety disorder (Pelletier et al., 2017).
• In the United States, among individuals with anxiety disorders, almost 15 per cent have a substance use disorder, and among individuals with substance use disorders, almost 18 per cent experience anxiety (McHugh, 2015).
• People with anxiety disorder are twice as likely to smoke tobacco as people who do not have a disorder (Kutlu et al., 2015).
    

Major depression

• In general, 15 to 20 per cent of all people will have major depression in their lifetime.
• Twenty-five per cent of people diagnosed with major depression are also diagnosed with substance use disorder. Among those, the most common substance used is alcohol (20 per cent), followed by unregulated substances (11.8 per cent) and cannabis (11.7 per cent) (Hunt et al., 2020).
• Compared with people with no diagnosis, people diagnosed with concurrent major depression and substance use disorders (i.e., alcohol, cannabis or other drugs) are at least 10 times more likely to have suicidal ideation, as well as other psychiatric con  -ditions (Onaemo et al., 2022; Davis et al., 2008).
    

Bipolar disorder

• In general, one to two per cent of all people will have bipolar disorder in their lifetime.
• Among people who have had bipolar disorder in their lifetime, around 90 per cent will also have a substance use disorder in their lifetime. Among those, the most common substances used are alcohol (62.3 per cent), cannabis (46 per cent), cocaine (24 per cent) and opioids (8.5 per cent) (Grunze et al., 2021).
    

Schizophrenia 

• One per cent of Canadians live with schizophrenia (Public Health Agency of Canada, 2020). 
• Among people who have had schizophrenia in their lifetime, 47 per cent will have a substance use disorder in their lifetime. 
    

2 Understanding concurrent disorders 

Concurrent disorders is a term for any combination of mental health and substance use problems. There is no symptom or group of symptoms that is common to all combinations. 

The combinations of concurrent disorders can be divided into eight main groups: 

1. Substance use and psychotic disorders: conditions that affect the mind, in which people have trouble distinguishing between what is real and what is not (e.g., schizophrenia). 
2. Substance use and impulsivity: problems of anger and aggression, including risk of harm to self or others 
3.  Substance use and mood disorders: conditions involving depression and affective instability (i.e., rapid and intense mood swings) (e.g., bipolar disorder) 
4. Substance use and anxiety disorders: features of excessive fear and anxiety and related behavioural disturbances 
5. Substance use and trauma- and stressor-related disorders: in which exposure to a traumatic or stressful event has caused a person to develop symptoms that bring about significant distress, behavioural disturbances and/or functional impairment.
     

How does each problem affect the co-occuring ones?

Some people with concurrent disorders have severe problems with both their mental health and their addictive behaviour. This makes it hard for them to function day-to-day. While other people may have milder co-occurring problems, the impact on their lives can still be quite negative.

Concurrent disorders may interact in several ways, such as: 

• substance use and/or other addictive behaviours can make mental health problems worse
• substance use and other addictive behaviours can mimic or hide the symptoms of mental health problems
• sometimes people turn to substance use to “relieve” or escape the symptoms of mental health problems
• some substances can make mental health medications less effective
• using substances can make people forget to take their medications, which can make the mental health problems come back (“relapse”) or worsen
• when a person relapses with one problem, it can trigger the symptoms of the other problem.

A person with concurrent disorders is at higher risk of experi-encing more serious medical, social and emotional problems than if they had only one condition. The interaction between the effects of substance use and mental health symptoms can prolong treatment and make it less effective. 

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