Effects of Rifaximin on Gut Microbiota and Emotion

This study is a randomized, triple-blind, placebo-controlled, interventional trial aiming to elucidate the impact of rifaximin-induced gut microbiota alteration to the psychobiological functioning of healthy men. The intervention will be performed in a parallel group design where one group will receive rifaximin (Targaxan 550 mg) twice daily for two weeks (treatment arm), while the other group will receive placebo (placebo arm).

Primary objective: to test the effect of rifaximin on stress sensitivity and fear-related processes

Secondary objective: to determine the mediating and/or moderating factors that underlie rifaximin-induced psychobiological changes

Inclusion criteria

• Voluntary written informed consent of the participant or their legally authorized representative has been obtained prior to any screening procedures
• Proficiency in English and/or Dutch
• Healthy with no intestinal and/or psychological complaints
• Access to a -18°C freezer (i.e. ordinary household freezer)
• Male participants
• Age 18-50 years
• BMI 18.5-25 kg/m2

Exclusion criteria

• Participant has a history of previous or current neurological, psychiatric, gastrointestinal or endocrine disorder
• Any disorder, which in the Investigator's opinion might jeopardize the participant's safety or compliance with the protocol
• Any prior or concomitant treatment(s) that might jeopardize the participant's safety or that would compromise the integrity of the Trial
• Participation in an interventional Trial with an investigational medicinal product (IMP) or device
• Hypersensitivity to the active substance rifaximin, to any rifamycin (e.g. rifampicin or rifabutin) or any of the excipients
• Current or recent medication use
• Use of antibiotics within three months preceding the study
• Current or recent (1-month) infection (e.g. common cold, influenza, COVID-19, etc.)
• Previous or current substance/alcohol dependence or abuse (>2 units per day or 14 units per week)
• One or more diagnoses based on the mini international neuropsychiatric interview (MINI-S)
• One or more diagnoses based on ROME IV for gastrointestinal disorders
• Smoking
• Night-shift work
• Adherence to special diets (e.g. vegan, vegetarian, weight-loss, lactose-free, gluten-free, etc.)
• Use of pre- or probiotics within one month preceding the study
• Previous experience with any of the tasks used in the study (not including questionnaires)
• Color vision deficiency (colorblindness)
• Magnetic Resonance Imaging (MRI) contraindications, including claustrophobia, severe back problems, conditions that would interfere with MRI scanning (e.g. cochlear implant, metal fragments in eyes, metallic body inclusion, or other metal implanted in the body), and if the participant does not want to be informed of incidental findings that might be found during imaging.