CYP2C19 and gastroesophageal reflux disease: In the case of GERD, a meta-analysis that included 19 studies demonstrated that the efficacy rates of PPIs varied significantly among CYP2C19 phenotypes (52.2% in NMs; 56.7% in IMs; 61.3% in PMs; p = 0.047) and that those subjects carrying a RM phenotype had an increased risk of being refractory to PPI therapy when compared with PMs (odds ratio = 1.7, 95% CI: 1.0–2.7) [86].