Effects of nVNS on Stress Reactivity in IBS

Open to people ages 18-50

• Age 18-50 years.
• Meets Rome V diagnostic criteria for IBS-D or IBS-M.
• At least moderate IBS symptom severity, defined as IBS-SSS ≥175.
• For females: premenopausal with generally regular menstrual cycles and willing to complete study visits within the study-specified menstrual-cycle window when feasible.
• Able to understand and provide informed consent in English.
• Willing and able to complete questionnaires, biospecimen collection, wearable monitoring, MRI procedures, and randomized study requirements.

• Individuals with obesity (BMI > 30).
• Evidence or history of another gastrointestinal disease that could explain symptoms, including inflammatory bowel disease or celiac disease, unless adequately excluded by clinical evaluation or prior testing.
• Pregnancy or a positive pregnancy test.
• Perimenopausal or postmenopausal status.
• Previous use in the last 3 months OR current use of hormonal medications, including hormonal contraceptives (i.e. birth control pills, patches, implants, or intrauterine devices (IUDs)) or hormone replacement therapy
• MRI contraindication, including a non-removable ferromagnetic implant or device, prior significant tattoo-related heating or burns, severe claustrophobia that cannot be managed, or another condition judged unsafe for MRI.
• Major active psychiatric illness (e.g., schizophrenia, bipolar disorder), significant neurologic or central nervous system disease, or another medical condition that could affect safety, adherence, or interpretation of study outcomes.
• Current participation in another IBS-specific intervention study or planned initiation of a new IBS-directed treatment during the 8-week randomized period.
• Contraindication to cervical nVNS or inability to use the device safely.
• Dermatologic conditions affecting the neck region that would interfere with nVNS placement
• Any implanted electrical device
• Any metallic device implanted at or near the neck
• History of cervical vagotomy
• Use of another electrical device at the same time (e.g., TENS unit, muscle stimulator) or any portable electronic device
• Movement disorder
• Clinically significant hypertension, hypotension, bradycardia, or tachycardia.
• Cardiac disease or atherosclerotic cardiac disease, including congestive heart failure, known severe coronary artery disease, or recent myocardial infarction within 5 years.
• Past abdominal surgery (except for appendectomy, cholecystectomy, benign polypectomy, hiatus hernia)
• Inability or unwillingness to provide informed consent or complete study procedures in English.