Abstract: A system for automatic feedback controlled administration of drugs (SAFCAD) is disclosed for the control of administration of drugs responsive to real-time processed physiological or pharmacological signals. Control apparatus implemented by analog, digital, or optimal-adaptive digital means is described using various combinations of proportional, integral and derivative control loop processes. A preferred digital embodiment uses optimal-adaptive, proportional-integral control which includes on-line physiological system modeling and control loop parameter tuning for the administration of anesthetics such as thiopental.