Previous studies have demonstrated that patient factors, like centralized pain and anxiety, are associated with increased pain and opioid consumption after a surgical procedure and with poor opioid efficacy.18,19,20 Furthermore, some genes have been implicated in opioid responsiveness, including the OPRM1 gene.21,22 These patient covariates were not measured in the present study and may account for some of the differences in the cohorts. Here, OPRM1 is linked to Anxiety.