Intestinal lumen

Diet  General dietary guidance: Eat in moderation; get adequate but not excessive fiber; decrease consumption of fatty and spicy foods; avoid caffeine, soft drinks, carbonation, and artificial sweeteners.A1,A2  Restricted diet: Diets restricted in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols may improve IBS symptoms in some patients, but questions remain regarding their long-term safety, effectiveness, and practicality.A3,A4  Gluten-free diet: The long-term effects of gluten-free diets on the microbiome and general nutrition are uncertain; they may lead to increased fat and sugar consumption. Strict gluten-free diets are expensive and difficult to follow and should be advised only for patients with proven celiac disease.A1,A5–A7

Probiotics  Probiotics, especially Bifidobacterium infantis, improve bloating, gas, and pain in IBS and may also help chronic idiopathic constipation.A1,A8

Exercise  Regular daily exercise decreases symptoms of IBS and chronic idiopathic constipation.A1

Fiber  Soluble fiber (psyllium; 25 to 30 g daily) provides a small benefit for some patients with IBS,A1,A8,A9 but it can also worsen bloating.  Insoluble fiber (bran, methylcellulose, calcium polycarbophil; two heaped teaspoons daily) is somewhat more effective for chronic idiopathic constipation than soluble fiber, but it can worsen bloating and flatulence in many patients.A8  Increase fiber gradually to minimize bloating, distention, flatulence, and cramping.A1,A8,A9  Worsening of gas and bloating suggests underlying dyssynergic defecation (pelvic floor dysfunction).A9

Osmotic laxatives  Polyethylene glycol (Miralax; 17 g once daily) is the osmotic laxative best studied and most effective for chronic idiopathic constipation.A8,A10  Other osmotic laxatives include lactulose, sorbitol, and mannitol.

Proton pump inhibitors  Proton pump inhibitors are recommended as empiric therapy in patients with functional dyspepsia who are Helicobacter pylori negative or who remain symptomatic after H. pylori eradication.A11,A12

Bowel wall

Opioid agonists  Loperamide (2 to 4 mg up to four times daily) decreases colonic transit and increases water absorption, improving many symptoms of diarrhea-predominant IBS.A8  Diphenoxylate/atropine (Lomotil) has not been studied in IBS.A8

Antispasmodics  Hyoscyamine (Levsin; 0.125 to 0.25 mg three times daily, 30 minutes before meals) is moderately effective for IBS.A9  Hyoscyamine, extended release (Levbid; 0.375 to 0.75 mg two times daily; maximum of 1.5 mg daily) is moderately effective for IBS.A9  Dicyclomine (20 mg four times daily, may increase to a maximum of 40 mg four times daily, 30 minutes before meals) is moderately effective for IBS.A9  Peppermint oil (200 to 750 mg two to three times dailyA8) is moderately effective for IBS.A9

Stimulant laxative  Stimulant laxatives (bisacodyl, cascara, senna) increase motility in chronic idiopathic constipation but may cause pain and diarrheaA8,A13,A14; they are usually reserved for patients with dysmotility disorders or opioid-induced constipation.

Prokinetic agents  Buspirone (Buspar; 5 to 10 mg three times daily, 30 minutes before meals), in addition to its antidepressant benefit, relaxes the gastric fundus and is effective for symptoms of functional dyspepsia.A15  Metoclopramide (Reglan), although approved for gastroparesis, has not been well studied in functional dyspepsia. Irreversible tardive dyskinesia can occur even at low dosages. It should not be used routinely for functional dyspepsia symptoms but may be considered after test-and-treat therapy, proton pump inhibitor therapy, and tricyclic antidepressant therapy.A11,A16

Neuromodulatory gut-brain axis

Tricyclic antidepressants  Amitriptyline (10 to 50 mg at bedtime; increase by 10 mg every one to two weeks) and other tricyclic antidepressants are moderately effective for symptom relief in diarrhea-predominant IBS and functional dyspepsia (histaminergic properties are moderately sedating; anticholinergic properties are moderately constipating).A10,A11,A17,A18

Central nervous system

Psychotropic drugs (e.g., selective serotonin reuptake inhibitors, serotonin-norepinephrine reuptake inhibitors) treat symptoms of underlying anxiety or depression but are less effective for associated pain and bloating.A17,A18 Psychological therapies (e.g., cognitive behavior therapy, hypnotherapy) improve quality of life and overall function in IBS and functional dyspepsia but are less effective for associated pain and bloating.A17,A18