Moreover, a correlation analysis revealed a negative relation between depression and NT-4 (r = −0.330, p = 0.005), and a weak negative relation between anxiety and BDNF or NT-4 (r = −0.268, p = 0.023 or r = −0.259, p = 0.028) in METH addicts. This evidence concerns the gene BDNF and depressive symptom measurement.