Glucocorticoids (also referred to as corticosteroids) are adrenal steroid hormones with diverse physiological effects that can be anti-inflammatory, immunosuppressive and metabolic in nature. They also affect central nervous system function and the activity of other endogenous hormones. Glucocorticoids are regulated by a negative feedback loop involving the hypothalamic-pituitary-adrenal (HPA) axis (Figure 20.1). Cortisol is the main hormone secreted from the adrenal cortex following the activation of the HPA axis and is released during stressful situations such as when encountering emotional stress, infection, trauma and exercise. In addition to responding to stress stimuli, endogenous cortisol is released in an hourly pulsatile manner and exhibits a circadian rhythm with peak concentrations occurring at the onset of the daily activity period (Young et al., 2004; Son et al., 2011).