The normal duration of modvigil is 10 to 15 hours, contingent on the person's metabolism, dosage, and general health. Within 1 to 2 hours of ingesting a regular 200 mg dose, most users start to experience its effects, with peak concentration happening 2 to 4 hours later. Because of its lengthy duration, it is useful for treating diseases like narcolepsy, shift work sleep disorder, and sleep apnea that cause excessive daytime sleepiness. It is recommended to take it in the morning to prevent insomnia.