After initial telephone interview, eligible participants were invited to the laboratory for a screening session. Afterwritten informed consent, participants provided a saliva sample for DNA analyses and completed individual differences measures. Prospective genotyping was used to oversample for the A118G SNP of the OPRM1 gene in the experimental portion of the study(Ray and Hutchison, 2004; Ray and Hutchison, 2007). Prior to the infusion sessions, participants attended a physical examination. From the total 295 participants screened in the laboratory, 48 were enrolled based on OPRM1 genotype and alcohol dependence status and completed the physical exam. Of those, 45 were medically eligible, and 43 individuals were randomized. See Table 1 for demographics on the experimental sample (n = 43). The attrition from the screening sample of 295 to the randomized sample of 43 was the result of prospective genotyping for the G allele of the OPRM1 gene as well as the requirement that participants meet current criteria for alcohol dependence.
