Compared to HCs, heroin addicts have a higher level of DAO, ET, and DLA (10.97 ± 3.24 U/L vs. 13.54 ± 3.27 p < 0.0001; 18.22 ± 3.41 U/L vs. 20.83 ± 5.36 U/L p < 0.05; 7.92 ± 4.21 mg/L vs. 10.36 ± 5.01 mg/L p < 0.05; respectively, Table 1). This evidence concerns the gene DAO and heroin dependence.