Provigil 100 mg is most often used to treat excessive sleepiness caused by narcolepsy, obstructive sleep apnea, and shift work. Provigil belongs to the class of drugs called stimulants. It is easy to use and buy Provigil 200 mg online with any doctor's prescription. The usual recommended dose for adults is 200 mg taken orally once a day in the morning. If you are using Provigil to treat shift work sleep disorder, you should take it one hour before the start of your shift.