Editing Servier - Tianeptine Controversy (section)

==Mechanism of Action Controversy==
Initially, Servier promoted tianeptine as having a unique mechanism of action, claiming it enhanced serotonin uptake—directly opposite to the mechanism of selective serotonin reuptake inhibitors (SSRIs). This purported mechanism challenged the monoamine hypothesis of depression, as both serotonin uptake inhibitors (classical tricyclic antidepressants) and this supposed serotonin uptake enhancer (tianeptine) showed antidepressant activity. 

However, in 2014, researchers discovered that tianeptine actually functions as a full μ-opioid receptor (MOR) agonist, with EC50 values of 194±70 nM for human MOR and 641±120 nM for mouse MOR. It was also found to be a full δ-opioid receptor agonist, though with much lower potency, while showing no activity at κ-opioid receptors. This revelation significantly changed the understanding of tianeptine's mechanism of action and raised concerns about its potential for abuse.