Nortriptyline for the Treatment of Functional Dyspepsia

Inclusion Criteria: * Age 18-65 years; * A diagnosis of FD according to the Rome IV criteria; * Predicted CYP2D6 extensive metabolizer phenotype on the basis of CYP genotyping * Insufficient effect of first line treatment with proton pump inhibitors (twice daily) or prokinetics; * In the presence of alarm symptoms, patients are required to have undergone an upper gastrointestinal endoscopy (without evidence of organic disease), and have tested negative for Helicobacter pylori 2 years prior to inclusion; * Women in their fertile age (\<55 years old) must use contraception or be postmenopausal for at least two years. Exclusion Criteria: * Predicted CYP2D6 poor, intermediate or ultrarapid metabolizer phenotype on the basis of CYP genotyping * Evidence of current anxiety and/or depression disorder as defined by a score ≥ 10 on the GAD-7 and/or PHQ-9 questionnaire; * Current use or any previous use of psychotropic medication in the last 3 months prior to inclusion; * Inability to discontinue prokinetics, NSAIDs or opioids; * Using drugs of abuse; * Using more than 2 or 3 units of alcohol per day (females and males respectively) * Previous major abdominal surgery or radiotherapy interfering with gastrointestinal function: 1. Uncomplicated appendectomy, cholecystectomy and hysterectomy allowed unless within the past 6 months; 2. Other surgery upon judgment of the principle investigator; * History of gastric ulcer; * History of liver disease, cholangitis, achlorhydria, gallstones or other diseases of the gallbladder/biliary system; * History of epilepsy * History of glaucoma * Pregnancy or lactation.