Modafinil reduces extreme sleepiness due to narcolepsy and other sleep disorders, such as periods of stopped breathing during sleep (obstructive sleep apnea). It is also used to help you stay awake during work hours if you have a work schedule that keeps you from having a normal sleep routine (shift work sleep disorder).
This medication does not cure these sleep disorders and may not get rid of all your sleepiness. Modafinil does not take the place of getting enough sleep. It should not be used to treat tiredness or hold off sleep in people who do not have a sleep disorder.
It is not known how modafinil works to keep you awake. It is thought to work by affecting certain substances in the brain that control the sleep/wake cycle.