Comparison of amino acid concentrations between before and after SSRI treatment. (A) Arginine, asparagine, cystine (median value, left scale), and glutamine/glutamic acid ratio (median value, right scale) were increased after antidepressant treatment in Wilcoxon signed rank test. (B) Glutamic acid and glutamine/glutamic acid ratio were significantly changed after antidepressant treatment only in the response group, and not in the nonresponse group.