Modvigil 200 mg is commonly used to improve alertness for 12 to 15 hours. Depending on individual tolerance, metabolism, and sensitivity, some individuals may experience even longer periods of alertness. While it can keep you awake for longer periods of time, it is not a replacement for sleep. Prolonged wakefulness, even with Modvigil 200, can impair cognitive performance and cause weariness after the medicine wears down. Follow medical advise for safe usage and avoid taking Modvigil 200 to skip sleep on a regular basis.