Childhood ADHD predicted earlier marijuana use, but twin analysis suggests shared genetics rather than a causal link
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.
Quick Facts
What This Study 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.
Key Numbers
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 They Did This
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.
Why This Research 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 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.
What This Study Doesn't 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.
Questions This Raises
- ?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?
Trust & Context
- Key Stat:
- Identical twins with different ADHD severity had similar marijuana outcomes
- Evidence Grade:
- 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.
- Study Age:
- Published in 2018. Genetic research methods and understanding of ADHD-substance use links have continued to advance.
- Original Title:
- Associations between childhood ADHD, gender, and adolescent alcohol and marijuana involvement: A causally informative design.
- Published In:
- Drug and alcohol dependence, 184, 33-41 (2018)
- Authors:
- Elkins, Irene J, Saunders, Gretchen R B, Malone, Stephen M(2), Keyes, Margaret A, McGue, Matt, Iacono, William G
- Database ID:
- RTHC-01651
Evidence Hierarchy
Follows a group of people over time to track how outcomes develop.
What do these levels mean? →Frequently Asked Questions
Does ADHD cause marijuana use?
Probably not directly. While children with ADHD are more likely to use marijuana, this twin study found that when identical twins differed in ADHD severity, substance outcomes were similar. This suggests shared genetics and environment, not ADHD itself, primarily explain the link.
Are girls with ADHD at higher risk?
This study found that females with more hyperactivity-impulsivity had higher alcohol consumption and progressed further toward daily marijuana use than males with similar symptom levels.
Read More on RethinkTHC
Cite This Study
https://rethinkthc.com/research/RTHC-01651APA
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
MLA
Elkins, Irene J, et al. "Associations between childhood ADHD, gender, and adolescent alcohol and marijuana involvement: A causally informative design.." Drug and alcohol dependence, 2018. https://doi.org/10.1016/j.drugalcdep.2017.11.011
RethinkTHC
RethinkTHC Research Database. "Associations between childhood ADHD, gender, and adolescent ..." RTHC-01651. Retrieved from https://rethinkthc.com/research/elkins-2018-associations-between-childhood-adhd
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.