In each patient, the demographic factors and the genotype of S-mephenytoin 4'-hydroxylase (CYP2C19) will be checked and defined as poor metabolizer (PM), homologous (HomoEM) or heterologous extensive metabolizer (HeteroEM). Each patient is treated continuously with dexlansoprazole 60 mg per day or lansoprazole 30 mg twice daily for eight weeks. During this 8-week study period, each patient is requested to record their daily clinical symptoms of reflux esophagitis on a special sheet, including the severity of acid regurgitation (AR, score 0: free from symptoms; score 1: attack episodes < 5 times per day; score 2: 6-10 times per day; score 3: more than 10 episodes per day), heartburn (HB, score 0: absence of symptoms; score 1: tolerable events not interfering with daily work; score 2: intolerable events interfering with daily work, but not needing medication to relieve the symptoms; score 3: complaints interfering with the completion of daily work, or causing the patient to wake up during the night with cough, or combined with any other non-specific complaints). The patients are scheduled to return to clinics for drug refills, and to hand back daily symptom records at the end of the fourth and eighth week of treatment.