Evidence from twin studies supports the role of correlated genetic influences on use of alcohol and other drugs, as well as smoking, although to a lesser extent. For instance, Young et al36 report genetic correlations of 0.15-0.3 between alcohol, tobacco and cannabis use. Similarly, Koopmans et al49 reported that the genetic correlation between use of alcohol and tobacco is negligible during adolescence but is unmasked during early adulthood. Despite the reduced effect of shared genetic influences on tobacco use, Han et al50 found evidence for a heritable (48%) common predisposition to alcohol, tobacco and drug use during adolescence.
