How Much of Cannabis Use Is Genetic? A National Twin Study | Research

The takeaway

A nationally representative US twin study found that recent cannabis use was at least 60% heritable, with monozygotic twins showing much higher similarity than dizygotic twins or siblings.

Read this if you want to understand the role of genetics in who uses cannabis.

Cannabis use at least 60% heritable in national US twin sample

What the researchers found

Twin and sibling resemblance for cannabis use in the past year was substantial. Monozygotic (identical) twin pairs showed much higher concordance than dizygotic (fraternal) twin pairs, and dizygotic twins showed similar resemblance to non-twin siblings. Modeling suggested heritability of at least 60% for last-year cannabis use.

Family environmental factors possibly contributed to resemblance as well, but no evidence was found for a special twin-specific environment influencing cannabis use. The finding that dizygotic twins and non-twin siblings showed similar resemblance strengthened the interpretation that shared genes rather than shared twin-specific experiences drove the familial pattern.

Why it matters

This was the first nationally representative US twin study of cannabis use, addressing a limitation of three prior twin studies that used non-representative samples. The high heritability estimate (60%+) established that genetic factors substantially influence who uses cannabis, independent of cultural and environmental factors.

The numbers in context

Heritability was estimated at a minimum of 60%. The study included both monozygotic and dizygotic twin pairs plus sibling pairs from a national probability sample.

How the study worked

This was a twin study using a US national probability sample of twin and sibling pairs. Cannabis use in the past year was assessed by self-report questionnaire. Biometrical twin analyses compared monozygotic twins, dizygotic twins, and non-twin siblings to partition variance into genetic, shared environmental, and non-shared environmental components.

What this study cannot tell us

The study assessed only last-year cannabis use, not lifetime use, frequency, or dependence. Self-report questionnaires may underestimate cannabis use. Twin studies estimate heritability for a specific population at a specific time and may not generalize across cultural contexts where cannabis availability and norms differ.

How to read the evidence

This is a well-designed twin study using a nationally representative sample with appropriate biometric modeling, providing moderate-level evidence.

When this study was published

Published in 2002. Subsequent molecular genetic studies have begun identifying specific genetic variants associated with cannabis use.

The bigger picture

This study joined a growing body of twin research establishing that cannabis use has a significant genetic component. Subsequent genome-wide association studies have begun identifying specific genetic variants associated with cannabis use, though these explain only a small fraction of the heritability estimated by twin studies.

Questions still open

Which specific genes contribute to the heritability of cannabis use? Do the same genetic factors influence cannabis initiation and progression to heavy use or dependence? How does heritability of cannabis use compare across different cultural and legal contexts?

Common questions

Is cannabis use genetic?

This study estimated that at least 60% of the variation in cannabis use is attributable to genetic factors. This does not mean cannabis use is predetermined, but rather that genetic factors substantially influence the likelihood of use, likely through traits like novelty-seeking, impulsivity, and sensitivity to drug effects.

Does having a twin who uses cannabis mean you will too?

Not necessarily, but the risk is higher, especially for identical twins who share all their DNA. The study found much higher concordance in identical twins than fraternal twins, but environmental factors and individual choices also play important roles.

Read the original research

Cannabis use in the last year in a US national sample of twin and sibling pairs.

Psychological medicine, 32(3), 551-4

View on PubMed ↗

Citation

Kendler, K S; Neale, M C; Thornton, L M; Aggen, S H; Gilman, S E; Kessler, R C. (2002). Cannabis use in the last year in a US national sample of twin and sibling pairs.. Psychological medicine, 32(3), 551-4.