A physician who is concerned with the administration of anesthesia and then the condition of the patient who is under anesthesia: An anesthesiologist uses a drug or a gas to cause the loss of bodily sensations with or without loss of consciousness.

Anesthetics, administered by anesthesiologists, can affect the whole body by making the patient unconscious, and are called "general anesthetics". Anesthetics that cause a person to have no feeling in only one specific part of the body are called "local anesthetics".