IntroductionAdolescence is the peak period for the onset of using substances. The median age of onset for alcohol and tobacco use is 16–18 years world‐wide, and somewhat later for illicit drug use such as marijuana (18–19 years) and cocaine (21–24 years) . Low use of alcohol or tobacco are the most prevalent patterns . Using multiple substances and including illicit drugs ) is associated with different predictors and more problematic outcomes .The causal mechanisms behind substance use in adolescence are still largely unknown, but genetic influences are indicated. Molecular studies have shown several genetic variants associated with substance use (individual effect sizes typically low ), some also pointing to a more non‐specific liability for abuse and dependence among substance types .Genetically informative designs (twin and extended family studies), estimating the total effect of genetic and environmental influences in complex traits, have proved very useful in studying the structures behind substance use, abuse and dependence . Twin studies have demonstrated heritabilities of 40–70% for alcohol and illicit drug dependence . The heritability of substance use is smaller . Genetic sources explained approximately half the variation in life‐time use of any substance in young twins . An additive genetic component explaining approximately 60% of
Addiction – Wiley
Published: Jan 1, 2018
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