The Longitudinal Link: A Systematic Review of Childhood ADHD and Early Onset of Substance Use in Adulthood

Background and Aim Current clinical practice increasingly involves adolescents and adults with substance use disorder (SUD) who have a history of childhood ADHD. Literature shows a strong association between childhood ADHD and alcohol and cannabis use, with ADHD often worsening SUD outcomes. This review aims to assess the prevalence of childhood ADHD among adults with SUD through meta-analysis and compare the age of substance use onset between those with and without childhood ADHD.Design and Participants A systematic search of databases (PubMed/Medline, CINAHL, Scopus, Web of Science, Embase) identified studies reporting ADHD prevalence and SUD onset age. Both observational and interventional studies were included if they had participants with a childhood ADHD diagnosis or assessed retrospectively through self-report or interviews, along with SUD. After screening, 20 studies were included for meta-analysis. Study quality was assessed using Risk of Bias in Non-randomized Studies of Interventions (ROBINS-I) and observation study quality evaluation scales.Findings The meta-analysis found a childhood ADHD prevalence of 9.9% (95% CI: 6.1%–15.2%) in adults with SUD. Regarding onset age, individuals with childhood ADHD started using substances significantly earlier than peers: tobacco (MD = −1.43, 95% CI: −1.61 to −1.26, p < 0.00001), alcohol (MD = −1.03, 95% CI: −1.54 to −0.53, p < 0.0001), and cannabis (MD = −1.15, 95% CI: −1.51 to −0.78, p < 0.0001).Conclusion Childhood ADHD is common among adults with SUD and correlates with earlier substance use onset. The current findings highlight the need for early identification of ADHD and its role in understanding the trajectory of substance use.