Dual diagnosis refers to the coexistence of a mental health disorder and a substance use disorder in the same person. There is no single cause that explains this relationship; it is a complex phenomenon involving multiple factors.
Why are the two disorders linked?
Scientific evidence suggests that mental disorders and addictions share genetic and environmental factors, which increases vulnerability to suffering from both. Furthermore:
People with mental disorders develop addictions more easily and with greater severity.
Addictive substances alter brain function, potentially triggering or exacerbating mental disorders.
Some people use substances to alleviate psychiatric symptoms or reduce the side effects of medication, which can lead to addiction.
Key epidemiological findings
Population-based studies show that:
People with addiction are more likely to have mental health disorders, and vice versa.
The age at which problematic substance use begins (15–30 years) coincides with the most frequent onset of mental health disorders.
The greater the number of mental health disorders, the higher the level of substance use, severity and need for treatment.
The use of one substance increases the risk of using others.
The most accessible and cheapest substances are the most commonly used.
The typical pattern of initiation is: tobacco and alcohol → cannabis → other drugs.
The risk of developing an addiction is highest for tobacco, followed by heroin and cocaine, then alcohol, and finally cannabis and tranquillisers.
Dual Diagnosis
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What is dual diagnosis?
Models explaining comorbidity
Common factors
Impulsivity, genetics and environmental stress increase the risk of both disorders. Impulsivity plays a key role in addictions and in disorders such as ADHD or Antisocial Personality Disorder.
Secondary addiction associated with a mental health condition
People with mental health conditions are more vulnerable: given the same level of consumption, they develop an addiction sooner, and it tends to be more severe and persistent.
Mental disorders secondary to addiction
Chronic substance use can lead to mental disorders, such as psychotic episodes, depression or cognitive impairment. Alcohol, cocaine, cannabis and hallucinogens have a particularly significant impact on vulnerable individuals.
Two-way model
This model incorporates all of the above: the two disorders influence each other over time.
Implications for treatment
Dual diagnosis is associated with a poorer prognosis, a higher risk of violence and antisocial behaviour, and, in particular, poor adherence to treatment. Consequently, the most effective approach is the integrated model, in which a single therapeutic team addresses both disorders simultaneously, as opposed to sequential or parallel treatments.