Effects of rifaximin on gut bacteria and emotional responses

A Randomized, Triple-blind, Placebo-controlled Study on the Effect of Rifaximin on Psychobiological Functions in Healthy Men

Phase2; Phase3 Interventional Universitaire Ziekenhuizen KU Leuven · NCT05587036

This study is testing if the antibiotic rifaximin can change gut bacteria and affect how healthy men respond to stress and fear.

Quick facts

PhasePhase2; Phase3
Study typeInterventional
Enrollment60 (estimated)
Ages18 Years to 50 Years
SexMale
SponsorUniversitaire Ziekenhuizen KU Leuven Academic / other
Locations1 site (Leuven)
Trial IDNCT05587036 on ClinicalTrials.gov

What this trial studies

This interventional trial investigates how rifaximin, an antibiotic, alters gut microbiota and its subsequent effects on stress sensitivity and fear-related processes in healthy men. Participants will be randomly assigned to receive either rifaximin or a placebo for two weeks, with a focus on understanding the psychobiological changes induced by the treatment. The study employs a triple-blind design to ensure unbiased results, and aims to identify factors that may mediate or moderate these changes.

Who should consider this trial

Good fit: Ideal candidates are healthy male volunteers aged 18-50 with a BMI between 18.5-25 kg/m2.

Not a fit: Patients with a history of neurological, psychiatric, gastrointestinal, or endocrine disorders may not benefit from this study.

Why it matters

Potential benefit: If successful, this study could provide insights into the relationship between gut health and emotional well-being, potentially leading to new treatments for stress and anxiety.

How similar studies have performed: While the relationship between gut microbiota and mental health is an emerging field, this specific approach using rifaximin is relatively novel and has not been extensively tested in similar studies.

Eligibility criteria

Show full inclusion / exclusion criteria
Inclusion Criteria:

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

Exclusion Criteria:

1. Participant has a history of previous or current neurological, psychiatric, gastrointestinal or endocrine disorder
2. Any disorder, which in the Investigator's opinion might jeopardize the participant's safety or compliance with the protocol
3. Any prior or concomitant treatment(s) that might jeopardize the participant's safety or that would compromise the integrity of the Trial
4. Participation in an interventional Trial with an investigational medicinal product (IMP) or device
5. Hypersensitivity to the active substance rifaximin, to any rifamycin (e.g. rifampicin or rifabutin) or any of the excipients
6. Current or recent medication use
7. Use of antibiotics within three months preceding the study
8. Current or recent (1-month) infection (e.g. common cold, influenza, COVID-19, etc.)
9. Previous or current substance/alcohol dependence or abuse (\>2 units per day or 14 units per week)
10. One or more diagnoses based on the mini international neuropsychiatric interview (MINI-S)
11. One or more diagnoses based on ROME IV for gastrointestinal disorders
12. Smoking
13. Night-shift work
14. Adherence to special diets (e.g. vegan, vegetarian, weight-loss, lactose-free, gluten-free, etc.)
15. Use of pre- or probiotics within one month preceding the study
16. Previous experience with any of the tasks used in the study (not including questionnaires)
17. Color vision deficiency (colorblindness)
18. 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.

Where this trial is running

Leuven

Study contacts

How to participate

  1. Review the eligibility criteria above with your treating physician.
  2. Visit the official trial page on ClinicalTrials.gov for the most current contact information and recruitment status.
  3. Contact the listed study coordinator or principal investigator to request pre-screening. Pre-screening is free and never obligates you to enroll.
Conditions Healthy VolunteersStressFearRifaximinAnti-Bacterial AgentsInflammationShort-Chain Fatty AcidMicrobiota-Gut-Brain Axis
Last reviewed 2026-06-13 by the Find a Trial editorial team. Information on this page is for educational purposes and is not medical advice. Always consult qualified healthcare professionals about clinical trial participation.