Stack of Zopiclone sleeping pill boxes. This is a hypnotic agent used to treat insomnia. Zopiclone is a controlled substance in the United States, Canada and some European countries and may be illegal to possess without a prescription. 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 is known colloquially as a 'Z drug'. Other Z drugs include zaleplon (Sonata) and zolpidem (Ambien and AmbienCR). They were initially thought to be less addictive and less habit forming than benzodiazepines.