Gabapentin 400 mg is a prescription painkiller drug that is used to treat nerve pain. It works in the brain and central nervous system and helps your body to recover from pain. This medicine is also used with other medications to control seizures.If the doctor prescribes it to you then tell him about your medical history of breathing problems, heart disease, or any liver disease. If you ever faced any allergy from Gabapentin or other opioid medicine then you should tell your doctor.