COMT and Erythema: These variants’ significant impacts on frequency of occurrence of erythema (OPRM1 A/A 31%, A/G 15% and G/G 0%, p = 0.037, medium effect size = 0.202), vomiting (COMT G/G 11%, G/A 5%, A/A 22%, p = 0.031, medium effect size = 0.212) and erythema (COMT G/G 38%, G/A 16% and A/A 24%, p = 0.031, medium effect size = 0.210) in OXN patients as can be seen in Fig. 4.