Zopiclone is a novel hypnotic agent used in the treatment of insomnia. Zopiclone is also available worldwide under various other trade names. While it acts on the BZ¹ receptor and is a short-acting hypnotic agent, it is not a benzodiazepine (with which it shares a number of characteristics and effects), but a cyclopyrrolone derivative, belonging to a novel chemical class which is structurally unrelated to existing hypnotics.

Zopiclone, as traditionally sold worldwide, is a racemic mixture of two stereoisomers, only one of which is active. In 2005, the pharmaceutical company, began marketing the active stereoisomer eszopiclone This had the consequence of placing what is a generic drug in most of the world under patent control in the United States, although in that country, it is expected to be available in generic form by the year 2010. It is already available off-patent in a number of European countries as well as Brazil. The eszopiclone/zopiclone difference is in the dosage—the strongest eszopiclone derivative dosage contains 3mg of the therapeutic stereoisomer, whereas, the highest zopiclone dosage (7.5mg) contains 3.75mg of the active stereoisomer. The two agents have not been studied via head-to-head clinical trials to determine if any clinical differences exist (e.g., efficacy, side-effects, developing dependence on the drug, and safety, etc.).

Zopiclone is known colloquially as a "Z drug", Other Z drugs include zaleplon (Sonata) and zolpidem (Ambien and AmbienCR) and were thought in initial studies to be less addictive and less habit forming than benzodiazepines. This appraisal has shifted somewhat in the last few years, as cases of addiction and habituation have been presented. It is recommended that zopiclone is taken on a "when required" basis, and daily or continuous use of the drug is not usually advised