Modafinil is a drug for treating sleepiness due to narcolepsy, shift work sleep disorder, or obstructive sleep apnea that is sold under the brand name Provigil, among others. Though off-label use has been used as an alleged cognitive enhancer, evidence on its efficacy for this use is not conclusive. It is swallowed by mouth.

Headaches, anxiety, difficulty sleeping, and nausea are common side effects. Allergic reactions such as anaphylaxis, Stevens–Johnson syndrome, and hallucinations can be severe side effects. It is uncertain whether it is safe to use during pregnancy. In those with kidney or liver disorders, the amount of medicine used may need to be changed. For those with arrhythmia, extreme hypertension, or left ventricular hypertrophy, this is not recommended. It is not fully clear how it operates. One explanation is that the regions of the brain associated with the sleep cycle could be affected.

Modafinil was approved in the United States in 1998 for medicinal use. It is listed as a Schedule IV controlled substance in the United States. It is just a prescription drug in the United Kingdom. As a generic drug, it is available.

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