HTR1A and major depressive disorder: Moreover, quetiapine is also effective as an augmentation in the treatment of depressive episodes [7], which is attributed to its active metabolite norquetiapine and its high affinity for both the noradrenaline transporter (SLC6A2) and the serotonin receptor 1A (HTR1A), towards which it was shown to exhibit inhibitory and partial-agonistic activity, respectively [12,13].