A non-invasive, optical-based physiological monitoring system is disclosed. In an embodiment, the non-invasive, optical-based physiological monitoring system comprises an emitter configured to emit light into a tissue site of a living patient; a detector configured to detect the emitted light after attenuation by the tissue site and output a sensor signal responsive to the detected light; and a processor configured determine, based on the sensor signal, a first physiological parameter indicative of a level of pain of the patient.