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.
Read this if you're interested in how genetics connect behavioral problems in childhood to substance use in adolescence.
Shared genetic factors linked conduct problems to marijuana use 8 years later
What the researchers 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.
Why it 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 numbers in context
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 the study worked
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.
What this study cannot 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.
How to read the evidence
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.
When this study was published
Published in 2007. Genome-wide association studies have since identified specific genetic variants associated with cannabis use, further supporting the role of genetics.
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.
Questions still open
- 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?
Common questions
Does this mean some kids are genetically destined to use marijuana?
What is the difference between initiation and progression?
Read the original research
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
Citation
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.
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