The CNS effects of alcohol range from mild euphoria (high), to impaired coordination, to ataxia, decreased mentation, labile mood, to poor judgment, slurred speech, nausea and vomiting, and finally to respiratory failure, coma and death, depending on the dose imbibed (see Schuckit, 1995). The final level of impairment appears to depend on a number of factors including a persons’ gender, age, weight, prior experience with alcohol and level of tolerance (Schuckit, 1994). Another source of variation in response to alcohol is individual variation in alcohol metabolism (see Wall et al., 1992, 1997, 2005; Wall and Ehlers, 1995; Ehlers et al., 2003; Duranceaux et al., 2006). Other sources of the genetic variation in sensitivity and tolerance to alcohol not attributed to differences in alcohol metabolism are less well understood. Several studies have found moderate heritability for level of response to alcohol. In one study, heritability was found to be 60% for a composite sensitivity measure that was used during an alcohol challenge in twins (Heath et al., 1999). Correlations of level of response to alcohol using body sway and the Subjective
