The drug's localised effect may explain why it increases wakefulness without triggering the "wired" feeling of stimulants such as coffee and amphetamines. Surprisingly, tests also found that when the drug wore off, there was no noticeable need for an extended sleep to recover.

Critics of more widespread use of Provigil fear that the drug might give people a false sense that they can cheat their need for sleep, while in reality they may be accumulating a sleep debt that will ultimately harm them.