Buy Provigil Online is a prescription medication approved to improve wakefulness in adults suffering from narcolepsy, obstructive sleep apnea, or shift-work sleep disorder. The most common Provigil dosages are 100 mg and 200 mg tablets, taken in the morning or before a work shift as directed by a healthcare provider. Doctors may adjust doses based on individual response and medical Common Provigil side effects include headache, nervousness, nausea, and insomnia.