Pharmaceutical composition for oral administration comprising O-desmethyltramadol or a pharmaceutically acceptable salt thereof, wherein O-desmethyltramadol is (1S, 2S) -O-desmethyltramadol, or a combination of (1R, 2R) -O-desmethyltramadol and (1S, 2S) -O-desmethyltramadol, in which the pharmaceutical composition is a prolonged-release oral dosage form, and in which the oral extended-release dosage form has an in vitro dissolution rate selected from the group consisting of in between 15 and 74% of O-desmethyltramadol released after 1 hour； between 28 and 91% of O-desmethyltramadol released after 2 hours； between 38 and 101% of O-desmethyltramadol released after 3 hours； between 47 and 105% of O-desmethyltramadol released after 4 hours； between 59 and 105% of O-desmethyltramadol released after 6 hours； between 68 and 105% 10 of O-desmethyltramadol released after 8 hours； between 75 and 105% of O-desmethyltramadol released after 10 hours； between 79 and 105% of O-desmethyltramadol released after 12 hours； and 100% O-desmethyltramadol released after 24 hours； when measured using a USP Apparatus I Basket procedure at 75 rpm in 900 ml of 0.05 M phosphate buffer with a pH 7.2 at 37 ° C.Composición farmacéutica para administración oral que comprende O-desmetiltramadol o una sal farmacéuticamente aceptable del mismo, en la que el O-desmetiltramadol es (1S, 2S)-O-desmetiltramadol, o una combinación de (1R, 2R)-O-desmetiltramadol y (1S, 2S)-O-desmetiltramadol, en la que la composición farmacéutica es una forma de dosificación oral de liberación prolongada, y en la que la forma de dosificación oral de liberación prolongada tiene una tasa de disolución in vitro seleccionada del grupo que consiste en entre 15 y 74% de O-desmetiltramadol liberado después de 1 hora； entre 28 y 91% de O-desmetiltramadol liberado después de 2 horas； entre 38 y 101% de O-desmetiltramadol liberado después de 3 horas； entre 47 y 105% de O-desmetiltramadol liberado después de 4 horas； entre 59 y 105% d
