The levels of serotonin and nor-epinephrine are regulated by MAO-A in the brain, and thus, MAO-A inhibitors such as tranylcypromine and Phenelzine (irreversible and non-selective MAO-inhibitors) and moclobemide (reversible and selective MAO-A inhibitors) are used for treating depression [43]. This evidence concerns the gene MAOA and depressive symptom measurement.