Association of family income supplements in adolescence with development of psychiatric and substance use disorders in adulthood among an American Indian population.

CONTEXT In a natural experiment in which some families received income supplements, prevalence of adolescent behavioral symptoms decreased significantly. These adolescents are now young adults. OBJECTIVE To examine the effects of income supplements in adolescence and adulthood on the prevalence of adult psychiatric disorders. DESIGN Quasi-experimental, longitudinal. POPULATION AND SETTING A representative sample of children aged 9, 11, or 13 years in 1993 (349 [25%] of whom are American Indian) were assessed for psychiatric and substance use disorders through age 21 years (1993-2006). Of the 1420 who participated in 1993, 1185 were interviewed as adults. From 1996, when a casino opened on the Indian reservation, every American Indian but no non-Indians received an annual income supplement that increased from $500 to around $9000. MAIN OUTCOME MEASURES Prevalence of adult psychiatric disorders and substance use disorders based on the Diagnostic and Statistical Manual of Mental Disorders in 3 age cohorts, adjusted for age, sex, length of time in the family home, and number of Indian parents. RESULTS As adults, significantly fewer Indians than non-Indians had a psychiatric disorder (106 Indians [weighted 30.2%] vs 337 non-Indians [weighted 36.0%]; odds ratio [OR], 0.46; 95% confidence interval [CI], 0.30-0.72; P = .001), particularly alcohol and cannabis abuse, dependence, or both. The youngest age-cohort of Indian youth had the longest exposure to the family income. Interactions between race/ethnicity and age cohort were significant. Planned comparisons showed that fewer of the youngest Indian age-cohort had any psychiatric disorder (31.4%) than the Indian middle cohort (41.7%; OR, 0.43; 95% CI, 0.24-0.78; P = .005) or oldest cohort (41.3%; OR, 0.69; 95% CI, 0.51-0.94; P = .01) or the youngest non-Indian cohort (37.1%; OR, 0.66; 95% CI, 0.48-0.90; P = .008). Study hypotheses were not upheld for nicotine or other drugs, or emotional or behavioral disorders. The income supplement received in adulthood had no impact on adult psychopathology. CONCLUSION Lower prevalence of psychopathology in American Indian youth following a family income supplement, compared with the nonexposed, non-Indian population, persisted into adulthood.