Twin study identified five drug use patterns in mid-adulthood, with persistent polydrug use being highly heritable

What the researchers found

Five drug use classes emerged: no/low use (50%), desistant cannabis use (23%), desistant party drug use (18%), persistent prescription drug misuse (4%), and persistent polydrug use (5%). Persistent polydrug use was highly heritable (a2 = 0.94) and associated with conduct disorder (OR = 2.40) and antisocial personality disorder (OR = 3.27). Persistent prescription misuse was linked to depression (OR = 2.38) and lifetime suicide attempt (OR = 2.31).

Why it matters

Identifying distinct trajectories of drug use with different genetic contributions and psychiatric correlates could improve targeted prevention and treatment approaches rather than treating all substance use as a single phenomenon.

The numbers in context

3,785 twins/siblings (1,365 men, 2,420 women; mean age 32); five classes: 50% no/low, 23% desistant cannabis, 18% desistant party drug, 4% persistent prescription, 5% persistent polydrug; MZ concordance k=0.30-0.35 vs DZ k=0.19-0.20; polydrug heritability a2=0.94

How the study worked

Latent class analysis applied to self-reported current and past drug use data from 3,785 twins and siblings (mean age 32) in the Australian Twin Registry Cohort III. Biometric modeling compared monozygotic and dizygotic twin concordances. Logistic regression examined associations with psychiatric disorders.

What this study cannot tell us

Cross-sectional with retrospective recall of past use, which approximates but does not substitute for true longitudinal data. Australian sample may not generalize globally. Self-reported substance use. Small sizes for the persistent use classes (4-5%).

How to read the evidence

Large genetically-informed twin sample with sophisticated statistical methods, though cross-sectional recall limits causal inference.

When this study was published

Published in 2021 using Australian Twin Registry data.

The bigger picture

The high heritability of persistent polydrug use (94%) and its distinct risk profile from persistent prescription misuse suggest these are fundamentally different conditions with different biological and environmental drivers, challenging one-size-fits-all approaches to substance use treatment.

Questions still open

• What specific genetic variants drive the high heritability of persistent polydrug use? Could the desistant cannabis class (23%) represent a normative developmental pattern rather than a clinical concern?

Common questions

Read the original research

Typologies of illicit drug use in mid-adulthood: a quasi-longitudinal latent class analysis in a community-based sample of twins.

Addiction (Abingdon, England), 116(5), 1101-1112

Citation

Dash, Genevieve F; Martin, Nicholas G; Agrawal, Arpana; Lynskey, Michael T; Slutske, Wendy S. (2021). Typologies of illicit drug use in mid-adulthood: a quasi-longitudinal latent class analysis in a community-based sample of twins.. Addiction (Abingdon, England), 116(5), 1101-1112. https://doi.org/10.1111/add.15225

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