The investigators aim to evaluate ursochol as a therapy in functional dyspepsia. The objectives of the study are to evaluate the effect of ursochol on duodenal permeability and dyspeptic symptoms and on duodenal low-grade inflammation, bile acid composition, bile acid receptor expression, nutrient tolerance and intragastric pressure.

Cross-over, controlled, randomized, double blinded, placebo-controlled trial with a 4 week intake of ursodeoxycholic acid (ursochol) versus a 4 week intake of placebo and a 4 week washout period in between. Two study days are planned during week 4 and week 12. During the 14 weeks, the patients have to fill in a diary. And for 14 weeks in total, the patients have to discontinue intake of proton pump inhibitors, drugs effecting gastric motility and NSAIDs and replace their oral anticonception with non-oral anticonception. Every two weeks of the study the investigator will call the participants to see how they are/if they have any discomforts or side effects.

Functional dyspepsia patients will be recruited and screened for inclusion in the study. The participants will be asked to not take proton pump inhibitors, drugs effecting gastric motility and NSAIDs and oral anticonception for fourteen weeks. First, they will stop with their daily drug intake of PPIs and NSAIDs for two weeks, then they will take placebo or UDC for four weeks, two doses every day during lunch and dinner. Afterwards, there will be a washout period of four weeks, and again four weeks of UDC or placebo intake. The patients will receive a diary in which they describe their symptoms/discomforts every day for 14 weeks. All participants and the investigator will be blinded to the nature (UDC or placebo) of the pills. The random order in which a certain patient gets his pills has been decided by the pharmacy of UZ Leuven and is also unknown for the investigator (double blinded). During week two, four, six, eight, ten and twelve we will have a phone conversation with the patients to discuss their symptoms/discomforts.

During week four and week twelve, the patients will come to the hospital for one day after an overnight fast. First, they are asked to fill in a bundle of questionnaires concerning physical complaints, depression, anxiety (disturbances), pain/disease, body/interoceptive awareness, trauma/abuse and personality and to give a fecal sample that they've collected the day before. The fecal sample will be used to evaluate the gastrointestinal microbiota in FD patients. Then, two blood samples, to evaluate liver function parameters and bile acid synthesis, will be taken and an endoscopy will be performed. All endoscopies will be performed by an experienced endoscopist (Jan Tack) and nine duodenal biopsies (2 biopsies at a time) (Radial Jaw™3 with needle; outside diameter 2.2mm; Boston Scientific, 302 Parkway, Global Park, Heredia, Costa Rica) will be obtained. To measure the in vitro transepithelial resistance, 3 biopsies will be examined using an adapted mini-Ussing chambers system. After equilibration, the mucosal side of the tissue will be exposed to 4kDa FITC-dextran as a measure of paracellular permeability. A sample will be taken from the serosal side during 2h at 30min interval. The concentration of fluoresceïn will then be measured using a fluorescence plate reader. Also, two biopsies will be used for mRNA extraction and subsequent cDNA synthesis. This cDNA will be used to measure the gene expression of bile acid receptors by means of real-time RT-PCR. In addition, one biopsy will be prepared for immunohistochemistry and two will be used for western blot to measure changes in distribution/expression of the bile acid receptor proteins. One biopsy will be obtained to study ultrastructural alterations by transmission electron microscopy.

After the endoscopy, an aspiration catheter will be positioned in the duodenum. The position of the catheter will be briefly checked by fluoroscopy (typically 2-3 seconds, however never more than 15 seconds). After positioning of the catheter, it is fixed to the subject's chin and he/she is asked to take place in a chair for the remainder of the experiment. For one hour, every 15 minutes duodenal fluids will be collected during fasted state. Next, a high resolution manometry catheter (HRM) will be placed in the gastric fundus to measure intragastric pressure and a perfusion tube (OD 2 mm) will be introduced through the nose and positioned in the stomach. After positioning of the catheters, they are fixed to the subject's chin and he/she is asked to take place in a chair for the remainder of the experiment. After a stabilization period of 15 minutes, intragastric infusion of the nutrient drink (Nutridrink, Nutricia; 630 KJ, 6 g proteins, 18.4 g carbohydrates, and 5.8 g lipids per 100 mL) will start at a constant speed of 60 mL per minute (determined by an automated system using a peristaltic pump). Intragastric pressure will be measured with a 36-channel high resolution manometry system, through the intragastric manometry probe. At 1-minute intervals, the subjects will be asked to score their satiation using a graphic rating scale that combines verbal descriptors on a scale graded 0-5. At 5-minute intervals the volunteers will be asked to fill out a VAS for 11 dyspeptic symptoms. The intragastric infusion will be stopped as soon as the volunteers score maximally on one of the 11 epigastric symptoms or when a score of 5 is reached on their satiety scores. 10 minutes thereafter, the catheters will be disconnected and removed. After the nutrient drink infusion, duodenal fluids will be collected every 15 minutes for 1.5 hour during fed state. Finally, the last catheter is removed and the volunteer can go home.

Inclusion Criteria:

Men and women (age 18-60 years) who meet the Rome IV criteria for functional dyspepsia can participate in the study. For 14 weeks, patients need to discontinue their intake of proton pump inhibitors, drugs effecting gastric motility and NSAIDs. If a female participant takes oral anticonception, she has to switch to non-oral anticonception for this study. All participants will receive and sign a copy of the informed consent.

Exclusion Criteria:

• refused informed consent
• pregnant women or women who are breastfeeding
• diabetes mellitus
• celiac disease
• coagulation disorders/anticoagulant therapy
• not well functioning liver and gallbladder
• active stomach or gut ulcer
• biliary colic, calcified gallstones
• acute infection of gallbladder or bile ducts, bile duct obstruction
• intestinal disorders such as ulcerative colitis, Crohn's disease
• lactose intolerance
• allergies/sensitivity (asthma, allergic to bile acids, eczema, allergic rhinoconjunctivitis)
• Intake of oral anticonception, barbiturates, antacid, colestyramine or colestipol, nitrendipine, cyclosporine, ciprofloxacine, rosuvastatine.
• first degree relatives with celiac disease, Crohn's disease or type I diabetes mellitus Severe kidney malfunction