drug administration. Change scores for summed pain intensity ratings were computed by subtracting the post-drug summed score from the pre-drug summed score, such that larger values indicate a greater reduction in pain following morphine administration, thus greater analgesia. Subjects with one or two rare alleles T of rs563649 showed less analgesia than homozygotes for the major allele C, with P-values approaching statistical significance, ranging from 0.054 to 0.09 (Supplementary Material, Table S2).
