This is particularly true for selective serotonin reuptake inhibitors (SSRIs) whose efficacy in anxiety and depression has been linked to their agonistic action on the serotonin-1A receptor subtype (5-HT1A) [42–44], and the difference between their antidepressant and anxiolytic effect may depend on whether they act on pre-synaptic (anxiolytic) or post-synaptic (antidepressant) 5-HT1A receptors [45]. Here, HTR1A is linked to major depressive disorder.