English O-Desmethyltramadol O-Desmethyltramadol O-Desmethyltramadol English English M1 (O-Desmethyltramadol) O-desmethyltramadol O-Desmethyltramadol O-Desmethyltramadol O-Desmethyltramadol O-desmethyltramadol