Adverse childhood experiences and drug use in early adulthood: an analysis of the Growing Up in Ireland 1998 cohort

Background 
Adverse childhood experiences (ACEs) can negatively impact health, with effects persisting into adulthood. Research has also demonstrated physical and mental health associations with substance use. In this prospective study we explored ACE associations with drug use, including harmful drug use, in early adulthood.
Methods
This was a secondary analysis of Growing Up in Ireland (GUI), a nationally representative prospective cohort of young people born in Ireland in 1998. Data on eight ACEs were collected at ages 9, 13 and 17 years.  Outcomes at 20 years were harmful drug use, defined as a score of 2 or more on the CAGE screening tool,  cannabis use, and other illicit drug use. Logistic regression was used to analyse the effect of both cumulative exposure to ACEs and the eight individual ACEs, while controlling for sociodemographic factors. 
Results
Our study population included 4,729 young people who completed all four waves of GUI. One or more ACEs were reported by 57.6% of participants, ranging from 1.9% who had experienced a stay in foster or residential care to 30.5% who reported conflict between parents. Having a positive CAGE score at 20 years was significantly associated with drug taking or alcoholism in the immediate family (Adjusted odds-ratio (aOR) 2.28, 95% CI: 1.64–3.18), conflict between parents (aOR 2.09, 95% CI: 1.64–2.68), mental disorder in the immediate family (aOR 2.07, 95% CI: 1.51–2.82), divorce or separation of parents (aOR 1.59, 95% CI: 1.18–2.13) and experiencing the death of a close friend (aOR 1.42, 95% CI: 1.06–1.91). Cannabis and other drug use were also significantly associated with drug taking or alcoholism in the immediate family, conflict between parents and mental disorder in the immediate family. Risks of each outcome increased with ACE count. In participants reporting 3 or more ACEs (vs. 0 ACEs), adjusted odds ratios ranged from 2.06 (95% CI: 1.49–2.83) for cannabis use to 2.66 (95% CI: 1.96–3.61) for other drug use and 3.05 (95% CI: 2.14–4.36) for a positive CAGE. 
Conclusion
The odds of drug use and having a positive CAGE score in early adulthood is significantly increased if there is a history of ACEs, and this risk significantly increases with when there are multiple ACEs. Our findings suggest that children who grow up in households where there are substance use problems, mental health disorders and parental conflict are at particular risk of later drug use. Public health prevention measures to reduce the prevalence of ACEs may reduce drug use. 
 
*Growing Up in Ireland (GUI) is funded by the Department of Children, Equality, Disability, Integration and Youth (DCEDIY). It is managed by DCEDIY in association with the Central Statistics Office (CSO). Results in this report are based on analyses of data from Research Microdata Files provided by the Central Statistics Office (CSO). Neither the CSO nor DCEDIY take any responsibility for the views expressed or the outputs generated from these analyses.