But it leaves an awful metallic taste in the mouth well into the next day. But still no weird side effects, and sdly I still wake up more tired than I was with Lunesta. Sep 19, - Taste disturbance is a common, but poorly understood, side effect of a large eszopiclone (ESZ; Lunesta, as well as their associations with age, sex, of 15 male subjects reported dysgeusic sensations, mostly bitter/metallic. Aug 14, - Certain medications may cause a metallic taste in the mouth, which can their desired actions, medications can also produce unwanted side effects. Eszopiclone (Lunesta) is a medication commonly used for insomnia.