Why Do Co-Occurring Disorders Happen?

There is no clear reason as to why co-occurring disorders happen.  There exists a relationship between substance use disorders and mental health disorders; however, there is no evidence to support that one causes the other even if one occurred first.  There are a few reasons as to why co-occurring disorders happen.

First, drugs and alcohol can cause a person to experience one or more symptoms of another mental health disorder simply by the drug used.  Marijuana has been found to increase the risk of psychosis in some individuals.  Second, a mental health disorder can lead a person to abuse drugs or alcohol.  Alcohol and drugs are often used to self-medicate the symptoms of a mental health disorder.  Third, both alcohol and drug disorders co-occurring with a mental health disorder are often the result of brain deficits, genetic vulnerabilities, or an exposure to trauma at a young age.

Genetic vulnerabilities are being researched as a possible reason for co-occurring disorders.  There are genes that might predispose a person to both a substance use disorder and a mental health disorder.  This vulnerability can stem from the complex interactions between multiple genes and from genetic interactions with one’s environmental influences.  Some genes can be altered depending on the drug used and how a person responds to the drug.  Genes can also influence how a person responds to stress whereby increasing the likelihood of drug-seeking behaviors.

Some areas of the brain are affected by both mental health disorders and substance-use disorders.  The neurotransmitter dopamine, is affected by both chemicals and mental health disorders such as depression.  Dopamine pathways can also be affected by stress and can increase vulnerability to substance use.  Stress is also a known factor for mental health disorders; therefore, this is one likely common link between mental health disorders and substance use disorders.

There is also evidence to support that certain areas of the brain that are involved in mental health and substance use disorders may overlap.  This overlap can precede the first symptom of a mental health disorder and can affect the onset of a substance use disorder.  If a mental health disorder develops first, changes in brain activity may increase vulnerability to substance use through enhancement of the positive effects of the substances used.  This can also reduce awareness of the negative effects of substances or alleviating the negative effects associated with the mental health disorder or the medication used to treat the mental health disorder.