Esmodafinil is the (S)-enantiomer of modafinil, a prescription drug used to improve wakefulness in patients with excessive sleepiness associated with narcolepsy, shift work sleep disorder, and obstructive sleep apnea. While esmodafinil and modafinil have the same molecular formula and similar physical properties, they differ in their biological activities. Esmodafinil is considered to be less potent than armodafinil, which is the (R)-enantiomer of modafinil, and is believed to have a different mechanism of action. Currently, esmodafinil is not approved for medical use and is not available as a prescription drug.
