Additionally, CYP2C19 rapid metabolizers who were prescribed first-generation proton pump inhibitors (PPIs), such as omeprazole for acid reflux treatment and other gastrointestinal disorders, may have experienced impaired PPI efficacy due to increased clearance of the drug, according to the respective CPIC guideline [33]. The gene discussed is CYP2C19; the disease is gastroesophageal reflux disease.