Genetic and environmental influences on cannabis use initiation and problematic use: a meta-analysis of twin studies.
Level 1 - systematic review of randomized trials
Systematic review and meta-analysis of twin studies (by design analogy, not clinical CEBM)
PubMed 20402985 · doi:10.1111/j.1360-0443.2009.02831.x
What was done
A systematic review and meta-analysis of twin studies evaluated the relative contributions of additive genetic factors (A), shared environment (C), and non-shared environment (E) to cannabis use initiation (28 studies) and problematic cannabis use (24 studies). Estimates of A, C, and E from independent cohorts were weighted by sample size and averaged separately for males and females.
What was found
For cannabis use initiation, variance accounted for by A, C, and E was 48%, 25%, and 27% in males, and 40%, 39%, and 21% in females. For problematic cannabis use, A, C, and E accounted for 51%, 20%, and 29% in males, and 59%, 15%, and 26% in females. Confidence intervals were narrower than those of individual source studies. A trend showed greater C and lesser A for cannabis initiation compared to problematic use in females.
Why it matters
This synthesis provides pooled quantitative estimates demonstrating that genetic factors account for approximately 40% to 59% of the variance in both cannabis initiation and problematic use. It also clarifies sex-specific patterns, showing shared environmental influences contribute more strongly to initiation than to problematic use in females.
Limits
The total number of individual participants was not reported in the abstract. Methodological assumptions inherent to classical twin modeling and specific diagnostic criteria for problematic use across source studies were not detailed.
Cited by
- supports The shared genetic heritability across most addictive substances is estimated to be approximately 0.3 to 0.5.