Fra Wikipedia: Zopiclone may be carcinogenic and mutagenic according to rat, mice and hamster studies. At 100 mg per kg of bodyweight per day, the experimental dosage was considerably higher than the therapeutic dose for humans. The authors of an uncontrolled study of zopiclone said that it may take decades in immunocompetent people before carcinogenic effects from past zopiclone use develops. It was suggested that further research and monitoring was required into the potential for zopiclone to cause cancer in immunocompetent patients.[45]

^ Stebbing J; Waters L, Davies L, Mandalia S, Nelson M, Gazzard B, Bower M (November 1, 2005). "Incidence of cancer in individuals receiving chronic zopiclone or eszopiclone requires prospective study". J Clin Oncol 23 (31): 8134–6. doi:10.1200/JCO.2005.03.5881. PMID 16258120.

Riktignok er dette ved ekstreme doser over tid, men allikevel.. hvorfor ikke velge noe som funker minst like bra uten å i seg selv kunne føre til kreft og uheldige cellemutasjoner?