Changing relationships between smoking and psychiatric disorders across twentieth century birth cohorts: clinical and research implications.

As the risks of tobacco use become recognized and smoking becomes stigmatized, new smokers may be increasingly driven to smoke by biological or genetic vulnerabilities rather than social desirability. Given that genetic risk for deviant proneness is shared across other psychiatric and addictive disorders, we predicted that as rates of smoking decreased through the latter half of the twentieth century, associations between smoking and psychopathology would increase. Participants (N=25 412) from a large US study-the National Epidemiologic Survey on Alcohol and Related Conditions, NESARC-were interviewed using the Alcohol Use Disorder and Associated Disabilities Interview Schedule - DSM-IV Version (AUDADIS-IV) and classified into one of five birth cohort decades (1940s to 1980s) and three smoking history (nonsmokers, never-dependent smokers and ever-dependent smokers) groups. We found that the prevalence of smoking decreased across the five birth cohorts, but associations of smoking with drug and AUDs, attention-deficit hyperactivity disorder, bipolar disorder and antisocial personality disorder, each increased monotonically in more recently born cohorts, even after adjusting for concurrent demographic and socioeconomic changes. For drug and AUDs, increases were observed among smokers both with and without a history of nicotine dependence; for other outcomes, increases were entirely driven by nicotine-dependent smokers. Findings suggest that smokers in more recent cohorts have disproportionately high psychiatric vulnerability, and may benefit from greater mental health screenings. Differentiating between casual and dependent smokers may further help prioritize those at greatest risk. Researchers should also be aware of potential variation in psychiatric comorbidity based on cohort of birth when defining groups of smokers, to minimize confounding.