The onset of substance use disorders most often occurs during the late teenage to early adult years, or roughly 18-27 years of age with mean age at 19.9 years according to epidemiologic surveys in the United States (US) (Kessler et al., 2005, Compton et al., 2007). Results from the 2012 US National Survey on Drug Use and Health reported that 19.7 years was the average age of onset for new US MA users (SAMHSA, 2013), which is similar to that for other illicit drugs. Since that report considered a population-based sample and ours a clinical sample of sufficient severity to require hospitalization, it is not surprising that age of onset in our sample tended to be earlier, although other factors could explain the difference-- for instance, the shifting trends of MA use in adolescent Thais. Prior studies of MA using populations have suggested potential differences between men and women. For example, although Brecht et al. (Brecht et al., 2004) found no sex differences in overall residential and outpatient US populations with respect to age of first MA use, they noted
