Modafinil is a wakefulness-promoting agent (or eugeroic) used for treatment of disorders such as narcolepsy, shift work sleep disorder, and excessive daytime sleepiness associated with obstructive sleep apnea. It has also seen widespread off-label use as a purported cognition-enhancing agent. In English-speaking countries it is sold under the brand names Alertec, Modavigil, and Provigil. In the United States modafinil is classified as a schedule IV controlled substance and restricted in availability and usage, due to concerns about possible addiction potential. In most other countries it is a prescription drug but not otherwise legally restricted.