Adverse childhood experiences (ACEs) describe different types of stressful or traumatic experiences during childhood, and exposure to extreme stress during critical periods of early life may increase the likelihood of exposure to a range of adverse factors.1 Importantly, studies have demonstrated positive associations between ACEs and substance use behaviours in young adults.2 However, many of these are based on cross-sectional data, which cannot provide evidence on the hypothesised direction of association between ACEs and substance use. In addition, the pathway between ACEs and substance misuse among emerging adults is not fully understood and few studies have investigated potential mediating factors.

Recent research conducted in Ireland examined ACE exposure associations with substance use behaviours using data from the Growing Up in Ireland study.3 Utilising a population-based longitudinal sample of 4,729 young people in Ireland recruited at age 9 years, the research had three aims. First, to describe the extent of ACE exposures among the sample population and the proportion who engaged in illicit substance use (current cannabis use, other illicit drug use, and problematic drug use) at age 20 years. Second, to examine individual and cumulative ACE exposure relationships with substance use behaviours. Third, to explore whether these associations are mediated by parent and peer relationships and liking school.

Notable findings from the study, which has been published in the journal Addictive Behaviors, include the following:

• Just over 30% of young adults had experienced two or more ACEs during the study period. With respect to drug use, 23.7% of participants indicated current cannabis use at age 20 years, while 27.9% used other illicit drugs. Just under 15% of young adults had a Cutting down, Annoyance by criticism, Guilty feeling and Easing of withdrawal symptoms (CAGE) score of 2 or more, suggesting problematic drug use.
• Regarding individual ACEs, significant associations with substance use behaviours were noted for young adults who had experienced conflict between parents and for those who had endured mental health disorders and drug taking/alcoholism in their immediate family.
• Significant dose–response relationships were also observed between the number of ACEs and substance use, with study participants who had experienced two ACEs or three or more ACEs having an approximate twofold and approximate threefold increased odds of problematic drug use, respectively, when compared with participants who had experienced no ACEs during the study period.
• Mediation analyses suggested that parent and peer attachment and liking school partially mediate relationships between ACEs and substance use behaviours in young adults. 

The authors suggest that prevention programmes which aim to reduce illicit substance use among young adults with traumatic childhood experiences should target children who have experienced parental conflict, mental illness, and substance use disorders in their families, as well as multiple ACEs, as these children are at a high risk of future substance use and problematic drug use. In supporting these children, identified mediators such as interpersonal relationships and school engagement may help guide selection of prevention interventions.

1    Pitts C, Millar SR, Perry IJ and Phillips CM (2024) Relationships between childhood adversity and inflammatory biomarkers in adulthood: A cross-sectional analysis of a middle-to older-aged population. SSM Popul Health, 25: 101608. Available from: https://www.drugsandalcohol.ie/43345/

2    Grummitt L, Barrett E, Kelly E and Newton N (2022) An umbrella review of the links between adverse childhood experiences and substance misuse: what, why, and where do we go from here? Subst Abuse Rehabil, 13: 83–100. Available from: https://www.drugsandalcohol.ie/37495//

3    Mongan D, Millar SR, Brennan MM, Doyle A, Galvin B and McCarthy N (2025) Associations and mediating factors between adverse childhood experiences and substance use behaviours in early adulthood: a population-based longitudinal study. Addict Behav, 161: 108194. Available from: https://www.drugsandalcohol.ie/42204/