Abstract: A system for controlling administration of a respiratory depressant drug or mixture of drugs to a spontaneously breathing patient comprises a drug delivery unit (3), being adapted for indexed or continuous and automatic titration of a respiratory depressant drug or mixture of such drugs to said patient (1), and a control apparatus (6), receiving measurement signals (20) relative to the respiratory state of said patient (1) and issuing control signals (27) to said drug delivery unit (3), wherein the control apparatus is adapted to keep said measurement signals relative to the respiratory state to a predetermined condition and thereby providing adequate sedation and/or analgesia to said patient.