Patients suffering from pruritus had significantly lower levels of β-endorphin (49.5 ± 5.9 pg/ml, Figure 2A) and dynorphin A (21.8 ± 2.6 pg/ml, Figure 2B) compared to patients without pruritus and healthy subjects, whereas the MOR/KOR-ratio was unaltered (Figure 2C). This evidence concerns the gene OPRM1 and Pruritus.