Recently, it has been revealed that tianeptine is a μ-opioid receptor (MOR) agonist and the hypothesis has been presented that precisely the MOR activation is the initial molecular event responsible for modulation of the glutamatergic system and for triggering many of known acute and chronic effects of tianeptine, including its antidepressant/anxiety actions (Gassaway et al. 2014). Here, OPRM1 is linked to Anxiety.