Genetic Evidence Suggests ADHD Causes Increased Cannabis Use, Not the Other Way Around
Mendelian randomization using genetic data from the largest available genome-wide studies found evidence for causal pathways from ADHD liability to smoking and cannabis initiation, but not convincingly in the reverse direction.
Quick Facts
What This Study Found
Genetic liability to ADHD increased the likelihood of smoking initiation, heavier smoking, difficulty quitting smoking, and cannabis initiation. There was weak evidence for ADHD increasing alcohol dependence risk. In the reverse direction, weak evidence for smoking initiation increasing ADHD risk was likely due to horizontal pleiotropy rather than true causation.
Key Numbers
Causal pathways confirmed from ADHD to: smoking initiation, cigarettes per day, reduced smoking cessation, cannabis initiation; weak evidence for ADHD to alcohol dependence; weak but likely confounded evidence for smoking to ADHD; no causal pathways between ADHD and coffee consumption.
How They Did This
Bidirectional Mendelian randomization using summary-level data from the largest available genome-wide association studies on ADHD, smoking, alcohol, cannabis, and coffee, with inverse-variance weighted regression and five sensitivity analyses.
Why This Research Matters
This genetic causal inference method avoids the confounding that plagues observational studies. Finding that ADHD liability causes increased substance use, rather than the reverse, has direct implications for prevention: treating ADHD may help prevent substance use.
The Bigger Picture
If ADHD is a causal driver of substance use rather than a consequence, early identification and treatment of ADHD could serve as a primary prevention strategy for substance use disorders.
What This Study Doesn't Tell Us
Mendelian randomization assumes genetic variants only affect the outcome through the exposure (no pleiotropy), which may not always hold; GWAS samples are predominantly European ancestry; cannot identify specific mechanisms linking ADHD to substance use.
Questions This Raises
- ?Would early ADHD treatment reduce cannabis and smoking initiation rates?
- ?What mechanisms mediate the causal effect of ADHD on substance use?
Trust & Context
- Key Stat:
- Genetic evidence supports causal pathways from ADHD to cannabis and smoking initiation
- Evidence Grade:
- Strong causal inference methodology using largest available GWAS data with multiple sensitivity analyses, limited by assumptions inherent to Mendelian randomization.
- Study Age:
- Published in 2021 using largest available GWAS data.
- Original Title:
- Investigating causality between liability to ADHD and substance use, and liability to substance use and ADHD risk, using Mendelian randomization.
- Published In:
- Addiction biology, 26(1), e12849 (2021)
- Authors:
- Treur, Jorien L(2), Demontis, Ditte(4), Smith, George Davey, Sallis, Hannah, Richardson, Tom G, Wiers, Reinout W, Børglum, Anders D, Verweij, Karin J H, Munafò, Marcus R
- Database ID:
- RTHC-03583
Evidence Hierarchy
Combines results from multiple studies to find an overall pattern.
What do these levels mean? →Frequently Asked Questions
Does ADHD cause cannabis use?
This study found genetic evidence supporting a causal pathway from ADHD liability to cannabis initiation, suggesting that the genetic factors underlying ADHD increase the likelihood of trying cannabis.
What is Mendelian randomization?
A method that uses genetic variants as natural experiments to test causal relationships. Because genes are determined at conception, genetic associations with ADHD are unlikely to be caused by substance use, allowing researchers to determine direction of causation.
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Cite This Study
https://rethinkthc.com/research/RTHC-03583APA
Treur, Jorien L; Demontis, Ditte; Smith, George Davey; Sallis, Hannah; Richardson, Tom G; Wiers, Reinout W; Børglum, Anders D; Verweij, Karin J H; Munafò, Marcus R. (2021). Investigating causality between liability to ADHD and substance use, and liability to substance use and ADHD risk, using Mendelian randomization.. Addiction biology, 26(1), e12849. https://doi.org/10.1111/adb.12849
MLA
Treur, Jorien L, et al. "Investigating causality between liability to ADHD and substance use, and liability to substance use and ADHD risk, using Mendelian randomization.." Addiction biology, 2021. https://doi.org/10.1111/adb.12849
RethinkTHC
RethinkTHC Research Database. "Investigating causality between liability to ADHD and substa..." RTHC-03583. Retrieved from https://rethinkthc.com/research/treur-2021-investigating-causality-between-liability
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.