A method and system for monitoring a patient under anesthesia involves determining a drug sensitivity index for the patient. Patient demographic information and amount of anesthetic information is obtained, wherein the amount of anesthetic information includes each drug administered to the patient and the dose amount thereof. An effect site concentration, which represents a total anesthetic concentration in a patient's brain, is then estimated based on the anesthetic information. An expected response is determined based on the demographic information and the effect site concentration. Physiological data is recorded from sensors mounted to a patient, and a depth of anesthesia is determined based on physiological data. An actual response of the patient is then determined based on the depth of anesthesia and the effect site concentration. Finally, a drug sensitivity index is determined for the patient by comparing the expected response to the actual response.