Armodafinil is a 2-[(diphenylmethyl)sulfinyl]acetamide that has R configuration at the sulfur atom. Like its racemate, modafinil, it is used for the treatment of sleeping disorders such as narcolepsy, obstructive sleep apnoea, and shift-work sleep disorder. Peak concentration in the blood later occurs later following administration than with modafinil, so it is thought that armodafinil may be more effective than modafinil in treating people with excessive daytime sleepiness. It has a role as a central nervous system stimulant and a eugeroic. It is an enantiomer of a (S)-modafinil.