Lunesta (eszopiclone) is used to treat insomnia in people over the age of 18. This medication can help you fall asleep faster and wake up fewer times during the night. Lunesta (eszopiclone) belongs to a drug class called sedative-hypnotics, and it's a controlled substance so there are restrictions on how it can be filled and refilled at the pharmacy. You typically only need to take a dose right before bedtime, but it can cause a headache or leave a bad taste in your mouth as a side effect.