The present invention relates to hydroxynorketamine for the use in the treatment of depression. In particular, the present invention concerns hydroxynorketamine for use in the treatment of depression, wherein hydroxynorketamine is administered in form of at least one prodrug, and wherein the at least one prodrug is orally administered in a modified-release dosage form. The prodrug is selected from (S)-Ketamine, (R)-Ketamine, (R,S)-Ketamine, (S)-Norketamine, (R)-Norketamine, (R,S)-Norketamine, (S)-Hydroxyketamine, (R)-Hydroxyketamine, (R,S)-Hydroxyketamine.
