Wiktionary
n. The active dextrorotatory stereoisomer of zopiclone, used as a sedative to treat insomnia.
Wikipedia
Eszopiclone, marketed by Sunovion under the brand-name Lunesta, is a nonbenzodiazepine hypnotic which is slightly effective for insomnia. Eszopiclone is the active dextrorotatory stereoisomer of zopiclone, and belongs to the class of drugs known as cyclopyrrolones.
Eszopiclone (Lunesta) along with other " Z-drugs" including zolpidem (Ambien), zaleplon (Sonata) are the most commonly prescribed sedative hypnotics in the United States. Eszopiclone is not marketed in the European Union following a 2009 decision by the EMA denying it new active substance status, in which it ruled that eszopiclone was too similar to zopiclone to be considered a new patentable product.
Eszopiclone is now available in a generic form in the United States as of May 2014. On May 15, 2014, the USFDA asked that the starting dose of Eszopiclone (Lunesta) be lowered from 2 milligrams to 1 milligram after it was observed in a study that even 8 hours after taking the drug at night, some patients were not able to cope with their next-day activities like driving and other activities that require full alertness.