Haas et al. [56] found that there were no significant differences in BDNF levels between patients taking no antidepressant treatments, patients taking analgesic doses of antidepressants, and patients taking antidepressants at therapeutic doses for depression (in pg/mL: group 1 = 130.4 ± 106.2; group 2 = 146.6 ± 137.9; group 3 = 194.0 ± 210.3, p-value = 0.81). This evidence concerns the gene BDNF and depressive symptom measurement.