(+)-modafinil is an enantiomer of modafinil, a wake-promoting agent, that primarily affects areas of the brain involved in controlling wakefulness. (+)-enantiomer of modafinil was clarified to be S-configuration. The optical enantiomers of modafinil have similar pharmacological actions. Both modafinil enantiomers bind in vitro to the dopamine transporter and inhibit dopamine reuptake with the R- slightly more potent than the S-enantiomer. As a component of racemic mixture (+)-modafinil is indicated to improve wakefulness in adult patients with excessive sleepiness associated with narcolepsy, obstructive sleep apnea/hypopnea syndrome, and shift work sleep disorder.