A twin study of 3,762 adolescents found that childhood ADHD predicted earlier marijuana initiation and faster escalation, but identical twin analysis suggested shared genetics and family environment, not ADHD itself, primarily drive the association.
Read this if you have ADHD or have a child with ADHD and want to understand the relationship between attention problems and marijuana use risk.
Identical twins with different ADHD severity had similar marijuana outcomes
What the researchers found
Researchers studied 3,762 twins (64% identical) to determine whether childhood ADHD causally leads to adolescent substance use or whether shared genetic and environmental factors explain the link.
Children with more severe ADHD symptoms initiated alcohol and marijuana use earlier, escalated to frequent or heavy use faster, and developed more symptoms of substance use problems by age 17.
Females with more hyperactivity-impulsivity had higher alcohol consumption and progressed further toward daily marijuana use than males with similar symptoms.
The critical test: when identical twins who differed in ADHD severity were compared, the twin with more severe ADHD did not have significantly worse substance outcomes than their co-twin. This pattern suggests that shared genetics and family environment, rather than ADHD itself causing substance use, primarily explain the association.
When other factors were controlled for, hyperactivity-impulsivity remained associated with both substances, and inattention remained specifically associated with marijuana but not alcohol.
Why it matters
This study uses a genetically informative design to address a fundamental question: does ADHD cause substance use problems, or do the same genes and environments that produce ADHD also increase substance use risk? The answer (mostly shared causes, not direct causation) has implications for prevention strategies.
The numbers in context
3,762 twins studied (64% identical). ADHD predicted earlier initiation and faster escalation to frequent use by age 17. Females with hyperactivity-impulsivity showed higher alcohol and marijuana use than males. Twin difference analysis: non-significant, suggesting shared etiology.
How the study worked
Three population-based twin samples (N=3,762, 64% monozygotic), including one oversampling females with ADHD. Childhood inattentive and hyperactive-impulsive symptoms predicted alcohol and marijuana outcomes by age 17. Twin difference analyses separated shared familial effects from within-pair (potentially causal) effects.
What this study cannot tell us
ADHD symptoms were assessed retrospectively or by parent report, not clinical diagnosis. Substance use was assessed by age 17, which may miss later-developing patterns. The study focused on symptom dimensions rather than categorical ADHD diagnosis. Twin studies assume equal environments for identical and fraternal twins, which may not perfectly hold.
How to read the evidence
This large genetically informative twin study provides strong evidence on the nature of the ADHD-substance use association, with rigorous methodology published in a top addiction journal.
When this study was published
Published in 2018. Genetic research methods and understanding of ADHD-substance use links have continued to advance.
The bigger picture
If ADHD itself caused substance use, treating ADHD should reduce substance use risk. But if shared genetics drive both, then prevention needs to target the underlying vulnerability rather than assuming ADHD treatment alone will prevent substance problems. This has significant implications for how clinicians approach substance use prevention in children with ADHD.
Questions still open
- Does treating ADHD with medication affect subsequent substance use risk? What specific shared genetic variants link ADHD and marijuana use? Why did inattention specifically predict marijuana but not alcohol use?
Common questions
Does ADHD cause marijuana use?
Are girls with ADHD at higher risk?
Read the original research
Associations between childhood ADHD, gender, and adolescent alcohol and marijuana involvement: A causally informative design.
Drug and alcohol dependence, 184, 33-41
Citation
Elkins, Irene J; Saunders, Gretchen R B; Malone, Stephen M; Keyes, Margaret A; McGue, Matt; Iacono, William G. (2018). Associations between childhood ADHD, gender, and adolescent alcohol and marijuana involvement: A causally informative design.. Drug and alcohol dependence, 184, 33-41. https://doi.org/10.1016/j.drugalcdep.2017.11.011
Explore the wider topic
- How to Talk to Your Teenager About Weed (Without Losing Them)
- My Kid's Friends Smoke Weed: A Parent's Guide
- I Smoke Weed But Don't Want My Kids To: Navigating the Hypocrisy
- Quitting Weed as a Parent: Why It Is the Hardest and Most Important Quit
- Quitting Weed as a Teen or Young Adult
- My Kid Is Smoking Weed: A Parent's Guide