Mental illness linked to substance use disorder transition

Research shows that there is a strong association between rates of transition from substance use to substance use disorder (SUD) and the lifetime risk for mental illness, particularly personality and psychotic disorders.

Shaul Lev-Ran (Centre for Addiction and Mental Health, Toronto, Ontario, Canada) and colleagues say their findings "can help guide clinicians in identifying patients at higher risk of developing a SUD after initial exposure to a substance and assist in the organization of prevention services."

The study, reported in The American Journal on Addictions, included data from the National Epidemiological Survey of Alcohol and Related Conditions of 43,093 adults with a lifetime prevalence of substance use.

Overall, 14,472 (33.7%) people in the sample had a mental illness during their lifetime, with a lifetime prevalence of 19.5% for mood disorders, 17.2% for anxiety disorders, 14.8% for personality disorders, and 0.78% for psychotic disorders.

The authors found that, compared with those without mental illness, people with a lifetime mental illness diagnosis were three times more likely to transition from nicotine use to SUD, while transition to SUD in these patients was 2.1- 1.7-, 2.5-, and 2.1-fold more likely for cannabis, cocaine, alcohol, and hallucinogens, respectively.

Lifetime diagnoses of psychotic disorders and personality disorders were particularly associated with high rates of transition from substance use to SUD, the authors note.

Among individuals without any lifetime diagnosis of mental illness, the rate of transition from substance use to SUD was lower for nicotine than the rate of transition for cocaine and cannabis. However, among those with a diagnosis of mental illness, rates of transition were highest for nicotine.

This may be because nicotine is involved in the pathogenesis of psychiatric disorders, or it may be used for self-medication in patients with mental illness, the authors suggest. It may also be that the same intrinsic factors, such as genetics, that dispose individuals to psychiatric illness are also associated with the tendency to maintain long-term smoking.

The authors say that their cross-sectional study was unable to examine temporal trends in substance use, and that further research will be needed. They also suggest that the research should be repeated in an adolescent population, who are particularly vulnerable to developing SUD after substance exposure.

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