An Early Phase 1 interventional study of Mirtazapine and Placebo in IBS - Irritable Bowel Syndrome and Diarrhea, sponsored by Mayo Clinic. Recruiting at 1 site in United States. Open to participants aged 18 Years to 70 Years. Per ClinicalTrials.gov, last updated 2025-12-18.
Sponsored by Mayo Clinic · Early Phase 1, Interventional, and Treatment
The purpose of this research is to study the added benefit of treating IBS symptoms with a medication called mirtazapine in treating IBS symptoms when paired with a low-FODMAP diet compared to a low-FODMAP diet alone. FODMAP stands for fermentable oligosaccharides, disaccharides, monosaccharides, and polyols. These are short-chain carbohydrates that can cause digestive distress in some people.
You have been asked to take part in this research because you have symptoms of diarrhea-predominant irritable bowel syndrome that may respond to treatment with a combination of a medication called mirtazapine and a low-FODMAP diet.
We hypothesize that adult patients with IBS-D treated with a combination of a low FODMAP diet and mirtazapine will have a greater improvement in global IBS symptoms including abdominal pain and diarrhea in addition to improved quality of life compared to those treated with a low-FODMAP diet only. Global improvement in IBS symptoms will be evaluated using the validated IBS-SSS questionnaire. We will evaluate changes in quality of life using a validated IBS-QoL questionnaire. We will assess the improvement in abdominal pain using a numerical rating system and assess improvements in diarrhea using the Bristol stool form scale. We will assess responses to bloating using a Mayo bloating questionnaire forms. We will assess improvement in diarrhea using the Bristol stool form scale.
Improvement in anxiety and any other descriptive information as provided by patients including patients reporting impression of overall severity of symptoms at the beginning, middle, and end of study.
Irritable bowel syndrome (IBS) is a common gastrointestinal (GI) disorder that affects up to 10% of the United States adult population. IBS is characterized by recurrent abdominal pain and altered bowel habits, diagnosed using the Rome IV criteria. Approximately one-third of all IBS patients are classified as having IBS with diarrhea (IBS-D), which has no validated treatment algorithm. The American College of Gastroenterology IBS guideline recommends the low-FODMAP (fermentable oligo-, di-, monosaccharide, and polyol) diet as a safe and modestly effective treatment. An analysis of 7 randomized, controlled trials found that the low-FODMAP diet was associated with an improvement in global IBS symptoms. However, despite following the low-FODMAP diet, many patients have persistent abdominal pain, which can be difficult to treat. The mechanisms underlying chronic abdominal pain in patients with IBS are unknown, although visceral and central hypersensitivity are thought to play a role. No medication is FDA-approved for the treatment of abdominal pain in IBS. Mirtazapine is an atypical antidepressant that acts on several classes of receptors. In a small open-label study mirtazapine improved IBS-D symptoms, including abdominal pain.
1,116 studies on the registry are indexed under Irritable Bowel Syndrome; 208 are open to participants now.
This study's planned enrollment of 20 is below the median of 70 across 896 interventional studies indexed under Irritable Bowel Syndrome.
Browse Irritable Bowel Syndrome studies →Mayo Clinic is the lead sponsor of 3,269 studies on the registry; 672 are open to participants now.
Of its 452 completed or terminated interventional studies of FDA-regulated products, 321 (71%) have results posted.
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Participants must meet all of the inclusion criteria to participate in this study:
Exclusion Criteria:
All candidates meeting any of the below exclusion criteria at baseline will be excluded from study participation:
Subjects will present at Mayo Clinic through a doctor's appointment and a diagnosis of irritable bowel syndrome will be receiving mirtazapine by pill form.
Drug: Mirtazapine
Subjects will present at Mayo Clinic through a doctor's appointment and a diagnosis of irritable bowel syndrome will be receiving placebo by pill form.
Other: Placebo
mirtazapine will be told to use 1 pill 1 hour before bedtime for the first week (7.5 mg po q.h.s.), 2 pills before bedtime during the second week of therapy (15 mg po q.h.s.), 3 pills (22.5 mg po q.h.s.) 1 hour before bedtime for the third week, and 4 pills (30 mg po q.h.s.) 1 hour prior to bedtime for the remainder of the study.
Also known as: Remeron
Placebo will be told to use 1 pill 1 hour before bedtime for the first week (7.5 mg po q.h.s.), 2 pills before bedtime during the second week of therapy (15 mg po q.h.s.), 3 pills (22.5 mg po q.h.s.) 1 hour before bedtime for the third week, and 4 pills (30 mg po q.h.s.) 1 hour prior to bedtime for the remainder of the study.
Resolution of Irritable Bowel Syndrome
Evaluate global improvement in IBS symptoms using the validated IBS-SSS
Time frame: 49 days
Abdominal Pain Score
Assess improvement in abdominal pain using a numerical rating system
Time frame: 49 days
Stool Form Scale
Assess improvement in diarrhea using the Bristol stool form scale
Time frame: 49 days
Mayo Bloating Scale
Assess response to bloating using a validated Mayo bloating questionnaire
Time frame: 49 days
Plan to share: No
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Studies of the drug tested here: Mirtazapine