Peripheral nerve field stimulation (PNFS) may be controlled based on detected physiological effects of the PNFS, which may be an efferent response to the PNFS. In some examples, a closed-loop therapy system may include a sensing module that senses a physiological parameter of the patient, which may be indicative of the patient's response to the PNFS. Based on a signal generated by the sensing module, the PNFS may be activated, deactivated or modified. Example physiological parameters of the patient include heart rate, respiratory rate, electrodermal activity, muscle activity, blood flow rate, sweat gland activity, pilomotor reflex, or thermal activity of the patient's body. In some examples, a patient pain state may be detected based on a signal generated by the sensing module, and therapy may be controlled based on the detection of the pain state.