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.