Allotetrahydrocortisol-d5 is the deuterium labeled Allotetrahydrocortisol. Allotetrahydrocortisol (5a-Tetrahydrocortisol) is a metabolite of Cortisol. Cortisol is the main glucocorticoid in human. It is produced in adrenal cortex and plays a crucial role in many physiological processes[1][2].