The duration of Modafinil 200 mg varies on the dose taken, the user's age, level of smart pill tolerance, liver function, and other factors. The half-life of modafinil, which ranges from 200 mg, can last up to 15 hours. Modafinil can help those who suffer from narcolepsy, obstructive sleep apnea/hypopnea syndrome (OSAHS), or shift work sleep disorder (SWSD) stay awake during the day.