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Review
. 2010 Mar;105(3):417-30.
doi: 10.1111/j.1360-0443.2009.02831.x.

Genetic and environmental influences on cannabis use initiation and problematic use: a meta-analysis of twin studies

Karin J H Verweij  1 , Brendan P Zietsch, Michael T Lynskey, Sarah E Medland, Michael C Neale, Nicholas G Martin, Dorret I Boomsma, Jacqueline M Vink
Affiliations
Review

Genetic and environmental influences on cannabis use initiation and problematic use: a meta-analysis of twin studies

Karin J H Verweij et al. Addiction. 2010 Mar.

Abstract

Background: Because cannabis use is associated with social, physical and psychological problems, it is important to know what causes some individuals to initiate cannabis use and a subset of those to become problematic users. Previous twin studies found evidence for both genetic and environmental influences on vulnerability, but due to considerable variation in the results it is difficult to draw clear conclusions regarding the relative magnitude of these influences.

Methods: A systematic literature search identified 28 twin studies on cannabis use initiation and 24 studies on problematic cannabis use. The proportion of total variance accounted for by genes (A), shared environment (C) and unshared environment (E) in (i) initiation of cannabis use and (ii) problematic cannabis use was calculated by averaging corresponding A, C and E estimates across studies from independent cohorts and weighting by sample size.

Results: For cannabis use initiation, A, C and E estimates were 48%, 25% and 27% in males and 40%, 39% and 21% in females. For problematic cannabis use A, C and E estimates were 51%, 20% and 29% for males and 59%, 15% and 26% for females. Confidence intervals of these estimates are considerably narrower than those in the source studies.

Conclusions: Our results indicate that vulnerability to both cannabis use initiation and problematic use was influenced significantly by A, C and E. There was a trend for a greater C and lesser A component for cannabis use initiation compared to problematic use for females.

Keywords: cannabis; genetics; heritability; meta-analysis; twin research.

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Figures

Figure 1
Figure 1
Heritability estimates (i.e. proportion of variance accounted for by genetic influences (A)) and 95% confidence intervals for the studies used in the meta-analysis of cannabis use initiation for males (1a) and females (1b). The bottom line shows the weighted A estimate and 95% confidence intervals estimated in the present meta-analysis. Dotted lines show confidence intervals estimated by a logarithmic curve regression on the sample sizes.
Figure 1
Figure 1
Heritability estimates (i.e. proportion of variance accounted for by genetic influences (A)) and 95% confidence intervals for the studies used in the meta-analysis of cannabis use initiation for males (1a) and females (1b). The bottom line shows the weighted A estimate and 95% confidence intervals estimated in the present meta-analysis. Dotted lines show confidence intervals estimated by a logarithmic curve regression on the sample sizes.
Figure 2
Figure 2
Heritability estimates (i.e. proportion of variance accounted for by genetic influences (A)) and 95% confidence intervals for the studies used in the meta-analysis of problematic cannabis use for males (2a) and females (2b). The bottom line shows the weighted A estimate and 95% confidence intervals estimated in the present meta-analysis. Dotted lines show confidence intervals estimated by a logarithmic curve regression on the sample sizes.
Figure 2
Figure 2
Heritability estimates (i.e. proportion of variance accounted for by genetic influences (A)) and 95% confidence intervals for the studies used in the meta-analysis of problematic cannabis use for males (2a) and females (2b). The bottom line shows the weighted A estimate and 95% confidence intervals estimated in the present meta-analysis. Dotted lines show confidence intervals estimated by a logarithmic curve regression on the sample sizes.
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