Gabapentin 400 mg is a prescription medication used to treat nerve pain (neuropathy) and control certain types of seizures. It works by affecting the way the brain and nerves transmit pain signals, providing relief from conditions like diabetic neuropathy, shingles-related nerve pain, and fibromyalgia. Gabapentin is also used as an adjunctive treatment for seizures in conditions such as epilepsy. It should be taken as prescribed by a healthcare professional to minimize the risk of side effects and ensure effectiveness.