Twin Study Found Genetics Influence Both Conduct Problems and Later Marijuana Use, With a Small But Real Link Between Them
In over 1,000 twin pairs followed for 8 years, childhood conduct problems made a small but significant genetic contribution to adolescent marijuana use initiation and progression.
Quick Facts
What This Study Found
Using data from 1,088 adolescent twin pairs in Wales and England, researchers examined how genetic and environmental factors influence the path from childhood conduct problems to adolescent marijuana use.
Marijuana use initiation (whether someone tried it) was influenced by genetic factors, shared environment, and unique environment. Marijuana use progression (how frequently someone used after trying it) was influenced by genetic and unique environmental factors, but not shared environment.
For conduct problems, the presence or absence of problems was largely heritable, while the severity of problems was more environmentally influenced.
Multivariate modeling showed that childhood conduct problems made a small but statistically significant contribution to marijuana use risk 8 years later, suggesting some shared genetic vulnerability between behavioral problems and later drug use.
Key Numbers
1,088 adolescent twin pairs. 8-year follow-up (1996-2004). Marijuana initiation influenced by genetics + shared + unique environment. Marijuana progression influenced by genetics + unique environment only. Conduct problems contributed a small but significant genetic risk to later marijuana use.
How They Did This
Prospective longitudinal twin study (CaStANET cohort). Conduct problems assessed in 1996 via parent and teacher reports. Marijuana use self-reported in 2004. Novel modeling approach separated marijuana use initiation from progression. Genetic, shared environmental, and unique environmental influences were estimated.
Why This Research Matters
The finding that genetics partly explain the link between conduct problems and marijuana use challenges the assumption that bad behavior simply leads to drug use. Some of the same genetic factors that predispose to behavioral problems may also predispose to marijuana use, independent of a direct causal path.
The Bigger Picture
This study contributed to the understanding that the association between childhood behavioral problems and adolescent substance use is partly genetic in origin, not purely a consequence of social learning or peer influence. This has implications for prevention strategies.
What This Study Doesn't Tell Us
Self-reported marijuana use in adolescents may be unreliable. The 8-year gap between assessments leaves the developmental pathway largely unobserved. The "small but significant" contribution suggests many other factors are involved. The sample was predominantly white British.
Questions This Raises
- ?Which specific genes contribute to both conduct problems and marijuana use vulnerability?
- ?Could early intervention for conduct problems reduce marijuana use initiation even if the genetic vulnerability remains?
Trust & Context
- Key Stat:
- Shared genetic factors linked conduct problems to marijuana use 8 years later
- Evidence Grade:
- This is a well-designed twin study with a longitudinal design and novel statistical modeling, providing moderate evidence for genetic overlap between conduct problems and marijuana use.
- Study Age:
- Published in 2007. Genome-wide association studies have since identified specific genetic variants associated with cannabis use, further supporting the role of genetics.
- Original Title:
- The association between conduct problems and the initiation and progression of marijuana use during adolescence: a genetic analysis across time.
- Published In:
- Behavior genetics, 37(2), 314-25 (2007)
- Authors:
- Shelton, Katherine, Lifford, Kate, Fowler, Tom, Rice, Frances, Neale, Mike, Harold, Gordon, Thapar, Anita, van den Bree, Marianne
- Database ID:
- RTHC-00292
Evidence Hierarchy
Follows a group of people over time to track how outcomes develop.
What do these levels mean? →Frequently Asked Questions
Does this mean some kids are genetically destined to use marijuana?
No. Genetics contribute to risk but don't determine behavior. Environmental factors also played significant roles, and many children with conduct problems never use marijuana. Genetics is one piece of a complex puzzle.
What is the difference between initiation and progression?
Initiation is whether someone tries marijuana at all. Progression is how frequently they use it after trying. This study found these are influenced by somewhat different combinations of genetic and environmental factors.
Read More on RethinkTHC
Cite This Study
https://rethinkthc.com/research/RTHC-00292APA
Shelton, Katherine; Lifford, Kate; Fowler, Tom; Rice, Frances; Neale, Mike; Harold, Gordon; Thapar, Anita; van den Bree, Marianne. (2007). The association between conduct problems and the initiation and progression of marijuana use during adolescence: a genetic analysis across time.. Behavior genetics, 37(2), 314-25.
MLA
Shelton, Katherine, et al. "The association between conduct problems and the initiation and progression of marijuana use during adolescence: a genetic analysis across time.." Behavior genetics, 2007.
RethinkTHC
RethinkTHC Research Database. "The association between conduct problems and the initiation ..." RTHC-00292. Retrieved from https://rethinkthc.com/research/shelton-2007-the-association-between-conduct
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.