OPRK1 and major depressive disorder: Since the discovery of SA as the only known naturally-occurring, non-nitrogenous kappa opioid receptor (KOR) agonist (Figure 1b),[5] research leading to clinical use of SA as a potential novel medication for addiction,[6, 6, 7] depression management,[8] and as a neuroprotective agent for neonatal hypoxia/ischemia, as well as brain injury due to oxygen insufficiency arising from cardiac arrest and stroke has been described in recent literature[9].