Anesthetic, also spelled anaesthetic, any agent that produces a local or general loss of sensation, including pain. Anesthetics achieve this effect by acting on the brain or peripheral nervous system to suppress responses to sensory stimulation. The unresponsive state thus induced is known as anesthesia. General anesthesia involves loss of consciousness, usually for the purpose of relieving the pain of surgery. Local anesthesia involves loss of sensation in one area of the body by the blockage of conduction in nerves.