The invention provides a potassium competitive acid blocker (P CAB) for use in the treatment prevention and/or reduction of gastro esophageal reflux disease (GERD) symptoms in patients who are partial responders to a proton pump inhibitor (PPI). The P CAB may for example be selected from l [5 (2 fluorophenyl) l (pyridin 3 ylsulfonyl) lH pyrrol 3 yl] N methylmethanamine (vonoprazan) revaprazan (YH1855) YH4808 RQ 4 and CS 526 or a salt thereof.