No previous report has examined qualitative sex differences in adolescence. However, several reports show no evidence for quantitative sex differences for tobacco initiation, use, problem use and dependence, illicit drug use or abuse, and alcohol initiation, frequency of use, intoxication, problem use and frequency of intoxication during adolescence (Han et al. 1999; Viken et al. 1999; McGue et al. 2000; Rhee et al. 2003; Poelen et al. 2008). Additionally, two studies examined quantitative effects on a ‘ general vulnerability ’ to substance use in adolescence. One report showed no significant sex differences (Han et al. 1999) whereas the second reported increasing heritability estimates for males and increasing environmental variance for females on an ‘externalizing factor ’ (including nicotine, alcohol and illicit drug dependence) from age 17 to 24 (Hicks et al. 2007).
