elevated daily intake of heroin in dependent subjects, though they did not find a significant effect of genotype and heroin dependence (Shi et al., 2002). A positive response to initial drug exposure is typically associated with continued use and abuse. In a study investigating the relationship between initial drug response and OPRM1 SNPs, the G118 allele was not associated with positive or negative subjective responses to first-time heroin use (Zhang et al., 2007), suggesting that differences in rates of dependence may not be explained by differences in initial euphoric experience.
