Substance-use disorders (SUDs) are highly prevalent in adults with ADHD (Crunelle et al, 2018; Özgen et al, 2020); however, there is a lack of large, population-based studies on this issue, especially in the context of Canadian adults. This study involved a Canadian, population-based assessment to compare the prevalence of alcohol-use disorders, cannabis-use disorders, other drug-use disorder and any SUD in young adults with ADHD and those without ADHD (objective 1). Additionally, the study aimed to investigate the degree to which the association between ADHD and each type of SUD is attenuated by demographics, socioeconomic status, adverse childhood experiences and mental health factors (objective 2). Finally, the study aimed to identify factors other than ADHD that are associated with the four aforementioned types of SUDs among adults (objective 3).
This study analysed data obtained from the cross-sectional, nationally representative 2012 Canadian Community Health Survey-Mental Health (CCHS-MH) survey. The current study was based on a subsample of the CCHS-MH sample described above, comprising 6872 respondents aged 20–39 years with complete data on ADHD and substance use, as well as all the other variables included in the final analysis. There were 270 respondents who reported they had been diagnosed with ADHD and 6602 respondents who had not been diagnosed. Substance abuse or dependence (termed SUD by the authors) was determined by lifetime algorithms for alcohol, cannabis and drug abuse and/or dependence, based upon the World Health Organization’s Composite International Diagnostic Interview criteria. A fourth outcome was created from a combination of all three of these types of substance abuse or dependence.
The proportion of males was higher in the population of participants with ADHD (70.5%) compared with those without ADHD (49.8%). There were more participants aged 20–29 years compared with 30–39 years in the study population with ADHD (64.6% vs 35.4%, respectively), whereas the age distribution in the study population without ADHD was almost equal (49.6% vs 50.4% for participants aged 20–29 years and 30–39 years, respectively). The prevalence of SUDs was significantly higher (p<0.001) amongst those with ADHD compared with those without ADHD; any SUD was the most prevalent in both groups (49% vs 24%), followed by alcohol-use disorder (36% vs 19%), cannabis-use disorder (23% vs 10%) and, finally, other drug-use disorder (18% vs 5%).
Those with ADHD had higher odds of an alcohol-use disorder than those without ADHD (odds ratio [OR] 1.38 [95% confidence interval (CI) 1.05–1.81]), and controlling for a history of depression or anxiety resulted in the largest amount of attenuation in the relationship between ADHD and alcohol-use disorders, followed by adverse childhood experiences (ACEs) and socioeconomic status. Those with ADHD also had higher odds of a cannabis-use disorder than those without ADHD (OR 1.46 [95% CI 1.06–2.00]), and controlling for a history of depression or anxiety resulted in the largest amount of attenuation in the relationship between ADHD and cannabis-use disorders, followed by ACEs, socioeconomic status and smoking status. The odds of a drug-use disorder (other than cannabis) were doubled for those with ADHD compared with those without ADHD (OR 2.07 [95% CI 1.46–2.95]), and controlling for a history of depression or anxiety resulted in the largest amount of attenuation in the relationship between ADHD and a drug-use disorder, followed by ACEs and socioeconomic status. Finally, those with ADHD had higher odds of any SUD than those without ADHD (OR 1.69 [95% CI 1.28–2.23]), and controlling for a history of depression or anxiety resulted in the most attenuation in the relationship between ADHD and any SUD, followed by ACEs and socioeconomic status. Overall, history of depression and anxiety led to the largest attenuation of the ADHD–SUD relationship, followed by childhood adversities and socioeconomic status.
In the model controlling for all variables simultaneously, there were multiple factors, in addition to ADHD, associated with all four types of SUDs, including: male gender, white race, being aged 20–29 years as opposed to 30–39 years, reporting problems meeting basic expenses, current or former smoking status, experiencing childhood physical abuse, and having a history of depressive and/or anxiety disorders. Furthermore, both having no post-secondary education and having marital status of single, divorced or widowed were characteristics significantly associated with alcohol-use disorder (OR 1.33 [95% CI 1.17–1.51] and OR 1.27 [95% CI 1.11–1.45], respectively), other drug-use disorders (OR 1.39 [95% CI 1.12–1.71] and OR 1.35 [95% CI 1.08–1.69], respectively) and any SUD (OR 1.22 [95% CI 1.08–1.39] and OR 1.30 [95% CI 1.15–1.48], respectively), but not cannabis-use disorders (OR 1.01 [95% CI 0.85–1.19] and OR 1.12 [95% CI 0.94–1.33], respectively). Nevertheless, cannabis-use disorders were associated with parental domestic violence exposure (OR 1.36 [95% CI 1.03–1.78]), as were other drug-use disorders (OR 1.41 [95% CI 1.03–1.92]) and any SUD (OR 1.25 [95% CI 1.00–1.56]), but not alcohol-use disorders (OR 1.13 [95% CI 0.90–1.42]). Childhood sexual abuse was associated with other drug-use disorders (OR 2.12 [95% CI 1.53–2.93]) and any SUD (OR 1.53 [95% CI 1.19–1.95]).
There were a number of limitations associated with the current study. Firstly, the CCHS-MH dataset did not contain information on some potentially important confounders, such as family background variables. In addition, the exposure variable (ADHD) was based on self-report of a medical diagnosis; therefore, participants who had not been formally diagnosed with ADHD would have been misclassified as not having ADHD, which would bias the findings toward the null hypothesis.
The authors concluded that this study demonstrates a significant relationship between ADHD and SUDs, even when controlling for a wide range of potential explanatory factors. Furthermore, it was proposed that prevention programmes promoting mental health, while addressing childhood and socioeconomic adversities, should be prioritised following on from the findings of this study.
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Crunelle CL, van den Brink W, Moggi F, et al. International consensus statement on screening, diagnosis and treatment of substance use disorder patients with comorbid attention deficit/hyperactivity disorder. Eur Addict Res 2018; 24: 43-51.
Fuller-Thomson E, Lewis DA, Agbeyaka S. Attention-deficit/hyperactivity disorder and alcohol and other substance use disorders in young adulthood: findings from a Canadian nationally representative survey. Alcohol Alcohol 2021; Epub ahead of print.
Özgen H, Spijkerman R, Noack M, et al. International consensus statement for the screening, diagnosis, and treatment of adolescents with concurrent attention-deficit/hyperactivity disorder and substance use disorder. Eur Addict Res 2020; 26: 223-232.