Gabapentin 400 mg is a prescription medicine commonly used to help manage certain types of nerve pain and seizures. It works by influencing abnormal nerve activity and may help reduce pain signals traveling through the nervous system. While many people tolerate gabapentin well, side effects can occur, particularly when treatment is first started or when the dosage is increased. Understanding the possible gabapentin 400 mg side effects can help patients recognize what may be expected and when ...