Lunesta^® is a prescription medication that is used for treating insomnia in adults. The sleep medicine, which is taken immediately before bedtime, comes in tablet form and is available in three different strengths. Potential side effects of the drug may include headache, drowsiness, and unpleasant taste. Lunesta has proven to be effective in helping people fall asleep faster and stay asleep longer, but since the medication is potentially habit-forming and can be abused, it should be taken with caution.