Modafinil is a prescription medicine used to improve wakefulness in adults with excessive sleepiness associated with narcolepsy, obstructive sleep apnea, or shift work disorder. In obstructive sleep apnea, modafinil treats excessive sleepiness rather than the underlying airway obstruction. Available tablet strengths include 100 mg and 200 mg. Important warnings include serious skin reactions, allergic reactions, psychiatric symptoms, and potential abuse or dependence.