Substance abuse in parents and subsequent risk of offspring psychiatric morbidity in late adolescence and early adulthood: A longitudinal analysis of siblings and their parents

The effects of substance abuse on other family members are not fully established. We estimate the contribution of parental substance abuse on offspring psychiatric morbidity in late adolescence and early adulthood, with emphasis on the timing and persistency of exposure. We used a nationally representative 20% sample of Finnish families with children born in 1986–1996 (n = 136,604) followed up in 1986–2011. We identified parental substance abuse and offspring psychiatric morbidity from hospital discharge records, death records and medication registers. The effects of parental substance abuse at ages 0–4, 5–9 and 10–14 on psychiatric morbidity after age 15 were estimated using population averaged and sibling fixed effects models; the latter controlling for unobserved factors shared by siblings. Parental substance abuse at ages 0–14 was associated with almost 2-fold increase in offspring psychiatric morbidity (HR = 1.86, 95% CI 1.78–1.95). Adjustment for childhood parental education, income, social class and family type reduced these effects by about 50%, with some further attenuation after adjustment for time-varying offspring characteristics. In the sibling fixed effects models those exposed at 0–4 or 5–9 years had 20% (HR = 1.20, 95% CI 0.90–1.60) and 33% (HR = 1.33, 95% CI 1.01–1.74) excess morbidity respectively. Also in sibling models those with early exposure at ages 0–4 combined with repeated exposure in later childhood had about 80–90% higher psychiatric morbidity as compared to never exposed siblings (e.g. for those exposed throughout childhood HR = 1.81, 95% CI 1.01–3.25). Childhood exposure to parental substance abuse is strongly associated with subsequent psychiatric morbidity. Although these effects are to a large extent due to other characteristics shared within the parental home, repeated exposure to parental substance abuse is independently associated with later psychiatric morbidity.