A Randomized Crossover Trial of Bright Light Therapy in Irritable Bowel Syndrome

Inclusion Criteria * 18-65 years old * Irritable Bowel Syndrome based on Rome IV diagnostic criteria * Mild to severe IBS symptom severity based on IBS-SSS greater than or equal to 75 17. * Late chronotype based on the Munich Chronotype Questionnaire (Corrected Midpoint of Sleep \> 4:00h) 18 Exclusion Criteria * Subject that are pregnant or plan to become pregnant. * Night shift workers or people who have crossed more than 2 time zones in the previous 4 weeks. * Regular use of medications that affect intestinal permeability, and/or endogenous melatonin including metoclopramide, NSAIDs, beta blockers, antibiotics, psychotropic medications, hypnotics and exogenous melatonin products during 4 weeks prior to the study. * Any major organ disease - known renal impairment, diabetes, liver disease, or significant cardiac failure (NY classification stage III/IV), inflammatory bowel disease or celiac disease per chart review and/or medical history. * Diagnosis of narrow angle glaucoma or retinal disorders or demonstrated symptoms indicative of these diagnosis during the eligibility screening. * Moderate to severe depression (score ≥ 21 or any endorsement of suicidal intent on the Beck Depression Inventory) 19 * Sleep apnea (score high risk in 2 or more categories of the Berlin Questionnaire) 20 * Restless leg syndrome (score ≥ 15 on the IRLS Study Group Rating Scale) 21 * Inability or unwillingness of subject to sign an informed consent