Armodafinil is the enantiopure of the vigilance-promoting drug, or eugeroic, Modafinil (Provigil). It consists of just the (−)-(R)-enantiomer of the racemic Modafinil. The mechanism of action of armodafinil is poorly understood, but it has been shown to act as both an indirect dopamine receptor agonist and a dopamine reuptake inhibitor. Armodafinil is currently FDA-approved to treat excessive daytime sleepiness associated with obstructive sleep apnea, narcolepsy, and shift work disorder. It is commonly used off-label to treat attention deficit hyperactivity disorder, chronic fatigue syndrome, and major depressive disorder. It has been shown to improve vigilance in air traffic controllers. Armodafinil as an adjunctive therapy in adults with schizophrenia had failed to meet the primary endpoints, and the clinical program was subsequently terminated