Why do addiction and schizophrenia often co-occur?
Unfortunately, those who have schizophrenia have been shown to have more of a predisposition to addiction, especially substance use disorder.
Individuals with schizophrenia commonly experience co-occurring substance use disorders, with notably high prevalence rates. Alcohol use disorders are prevalent, with rates ranging from 21% to 86%, while cannabis and cocaine use disorders show prevalence rates of 17–83% and 15–50%, respectively. These figures are strikingly higher than those observed in the general population.
The elevated rates of substance use disorders in individuals with schizophrenia pose significant challenges. Co-occurring substance use disorders in this population have been linked to various adverse outcomes, including clinical exacerbations, non-compliance with treatment, poor global functioning, increased risk of violence, elevated suicide rates and higher rates of relapse and re-hospitalisation. These complications underscore the critical need for targeted interventions and support systems to address both the psychiatric and substance use aspects of individuals with schizophrenia.
So, why does this happen? According to research, sadly, there is no concrete answer. But, there are many theories put forward as to why schizophrenia and addiction co-occur so often.
Fowles (1992) & Museser et al. (1990)
The diathesis-stress model, also known as the “two-hit” model, suggests that a biological vulnerability interacts with environmental stressors, such as substance use, leading to schizophrenia (Fowles, 1992). Another related idea, the cumulative risk factor hypothesis, proposes that individuals with schizophrenia are more likely to develop substance use disorder due to the combined impact of poor cognitive, social, educational and vocational functioning, along with factors like poverty, victimisation and deviant social environments (Mueser et al., 1990).
Green et al. (1999) & Chambers et al. (2001)
An alternative biological theory, sometimes called the “primary addiction hypothesis” (Chambers et al., 2001) or “reward deficiency syndrome” (Green et al., 1999), proposes that schizophrenia and substance use disorders have a shared underlying biology in overlapping neural circuits. According to this theory, substance use in individuals with schizophrenia might be linked to dysfunction in the brain’s reward circuit.
Khantzian (1997)
The self-medication hypothesis is a prominent explanation for the elevated comorbidity rate observed in individuals with schizophrenia and substance abuse. This theory suggests that people with schizophrenia may turn to drug use as a way to cope with various aspects of their illness or to alleviate undesirable side effects associated with antipsychotic medications, such as dysphoric reactions or extrapyramidal symptoms.
In recent years, though, the self-medication hypothesis has declined in appeal and influence, partly overshadowed by the growing emphasis on fundamental neurobiological research.
