Eszopiclone vs Zopiclone: what is the difference?

How they differ

Eszopiclone is the S mirror image of zopiclone, so the two share the formula C17H17ClN6O3 and a weight of 388.8. Zopiclone, sold as Zimovane and Imovane in the UK and Europe, is an even mix of both forms, while eszopiclone, sold as Lunesta, is the active form isolated and the version approved in the United States. Neither is a benzodiazepine, but both act at the same GABA-A receptor, which is why they are grouped with zolpidem as the Z-drugs. They share a famous side effect, a bitter metallic taste, because the molecule is secreted into saliva.

Side by side

Structural similarity 1.00 of 1, computed as a Morgan fingerprint Tanimoto coefficient. It measures shape, not effect.

Common questions

What is the difference between Eszopiclone and Zopiclone?

Eszopiclone is the S mirror image of zopiclone, so the two share the formula C17H17ClN6O3 and a weight of 388.8. Zopiclone, sold as Zimovane and Imovane in the UK and Europe, is an even mix of both forms, while eszopiclone, sold as Lunesta, is the active form isolated and the version approved in the United States. Neither is a benzodiazepine, but both act at the same GABA-A receptor, which is why they are grouped with zolpidem as the Z-drugs.

Do Eszopiclone and Zopiclone have the same formula?

Yes. Both are C17H17ClN6O3 at 388.8 g/mol. They are isomers: the same atoms arranged differently, which is why they behave differently despite weighing the same.