Modafinil 200 mg is prescribed to treat conditions that cause excessive daytime sleepiness and disrupt normal daily functioning. It is most commonly used for narcolepsy, a neurological disorder that leads to sudden sleep episodes. Doctors also prescribe it for obstructive sleep apnea when fatigue persists despite primary treatment, and for shift work sleep disorder in people with irregular schedules. By promoting wakefulness, modafinil helps patients stay alert and maintain productivity during the day. While it does not cure these conditions, it plays an important role in symptom management when combined with proper medical care and healthy sleep habits.