Ambien is a brand name for the drug zolpidem, which is used to treat insomnia. It works by slowing down activity in the brain, allowing people to fall asleep more quickly and stay asleep longer. It is usually taken as a tablet or capsule and should be taken shortly before bedtime. Ambien is a commonly prescribed medicine for insomnia, but it can have side effects such as dizziness, drowsiness, and headaches.