Cannabis use in the last year in a US national sample of twin and sibling pairs.
BACKGROUND
Three prior population-based twin studies, none of which was nationally representative, suggested that both genetic and familial-environmental factors contribute to family resemblance for lifetime cannabis use. We seek to replicate these results in a US national probability sample of twin and sibling pairs examining only last year cannabis use.


METHODS
Cannabis use in the last year was assessed by self-report questionnaire. Biometrical twin analyses were performed.


RESULTS
Twin and sibling resemblance for last-year cannabis use was substantial, and much higher in monozygotic pairs than in dizygotic and sibling pairs, where levels of resemblance were similar. Modeling suggested that sibling resemblance was due to genetic factors--with a heritability of at least 60% and probably family environmental factors. No evidence was found that cannabis use was influenced by a special twin environment.


CONCLUSIONS
Consistent with prior studies, use of cannabis is substantially influenced by genetic factors but family-environment is also possibly of importance.
Kendler
K S
KS
Department of Psychiatry, Medical College of Virginia/Virginia Commonwealth University and Virginia Institute for Psychiatric and Behavioral Genetics, Richmond, USA.
Neale
M C
MC
Thornton
L M
LM
Aggen
S H
SH
Gilman
S E
SE
Kessler
R C
RC
D000328:Adult; D000368:Aged; D004200:Diseases in Twins; D005260:Female; D020022:Genetic Predisposition to Disease / Q000235:genetics; D006801:Humans; D008297:Male; D002189:Marijuana Abuse / Q000453:epidemiology / Q000235:genetics* / Q000523:psychology; D008875:Middle Aged; D009679:Nuclear Family / Q000523:psychology; D012307:Risk Factors; D012494:Sampling Studies; D012931:Social Environment; D014481:United States / Q000453:epidemiology