Psychoactive Drugs Tobacco, Alcohol, and Illicit Substances

5. Why do drug addiction and mental illness often coexist?

Individuals often suffer from drug problems in combination with depression
Source: Patrick Jan Van Hove

Drug addiction is more frequent in individuals who have a mental illness compared to individuals without any mental disorder. Likewise, people who are drug dependent are more likely to suffer from mental disorders than non-dependent people. This indicates either a shared neurobiological basis for both afflictions, or an interaction of effects at some level.

This may be explained by different hypotheses:

1. Drug dependence and mental illness may be based on the same processes in the nervous system.
2. Drug use may help to ease some of the symptoms of the mental illness or the side effects of medication.
3. Drug use may precipitate mental illnesses or lead to biological changes that are involved in mental illnesses.

There is some evidence for all of these hypotheses. For instance, many psychoactive drugs can produce psychiatric-like syndromes. For example, amphetamines and cocaine can induce psychotic-like symptoms. Hallucinogenic substances can affect perception, thinking, and feeling, and produce hallucinations, which are an aspect of some psychoses. Furthermore, psychoactive drug use regularly changes a person’s mood, producing either happy feelings or depressive symptoms, especially during withdrawal.

Research on the link between drug dependence and mental illness has only been carried out in a few countries and the results may not be applicable to other cultures.

For example, a US study has shown that people with mental disorders are 4.5 times more likely to be drug-dependent and 2.3 times more likely to be alcohol-dependent at some stage in their lives compared to people without any mental illness.

People who are dependent on drugs such as alcohol, tobacco, and cocaine have been shown to be more likely to suffer from mental disorders such as depression compared with non-dependent people. For instance, a US study has shown that 38 to 44% of people who are alcohol-dependent have suffered from major depression, compared with 7% in non-dependent individuals. More...