What are the recommended non‑pharmacologic and pharmacologic treatment options for irritable bowel syndrome, including IBS‑D, IBS‑C, and IBS‑M?

Treatment for Irritable Bowel Syndrome

Start with Lifestyle and Dietary Modifications for All Patients

All IBS patients should begin with regular physical exercise and soluble fiber supplementation (psyllium 3-4 g/day, gradually increased), while avoiding insoluble fiber like wheat bran which consistently worsens symptoms. 1, 2

Universal First-Line Interventions

• Prescribe regular moderate-intensity physical activity to every IBS patient, as this yields significant improvement in overall symptoms—particularly constipation—with benefits maintained for at least five years. 1, 2
• Provide clear explanation that IBS is a gut-brain interaction disorder with a benign, relapsing-remitting course (not progressive) to establish realistic expectations and reduce anxiety. 3, 1, 2
• Ensure adequate time for regular defecation and proper sleep hygiene. 3, 2

Dietary Management by Subtype

For IBS-C (Constipation-Predominant):

• Start soluble fiber (psyllium/ispaghula) at 3-4 g/day and titrate upward gradually to minimize bloating; this improves global symptom scores and abdominal pain. 1, 2
• Avoid insoluble fiber (wheat bran) in all IBS subtypes—it consistently aggravates bloating and worsens symptoms. 1, 2

For IBS-D (Diarrhea-Predominant):

• Reduce fiber intake and identify excessive consumption of lactose, fructose, sorbitol, caffeine, or alcohol. 3, 1
• Trial lactose exclusion if the patient consumes substantial lactose (>280 mL milk/day). 3, 1

For Refractory Symptoms (All Subtypes):

• Refer to a trained dietitian for a supervised low-FODMAP diet delivered in three phases: (1) restriction for 4-6 weeks, (2) systematic reintroduction, and (3) personalized maintenance based on individual tolerance. 1, 2
• Do not recommend gluten-free diets unless celiac disease is confirmed—current evidence does not support their use in IBS. 1, 2

Pharmacological Treatment: Target the Predominant Symptom

For Abdominal Pain and Cramping (All Subtypes)

• Use anticholinergic antispasmodics (dicyclomine) taken before meals as first-line therapy for meal-related abdominal pain; counsel patients about dry mouth, visual disturbances, and dizziness. 3, 1, 2
• Peppermint oil provides an alternative antispasmodic effect with a more favorable side-effect profile. 3, 1

For IBS-D (Diarrhea-Predominant)

• Loperamide 4-12 mg daily (regular dosing or prophylactically before outings) is first-line therapy to reduce stool frequency, urgency, and fecal soiling. 3, 1, 2
• Titrate the dose carefully to prevent constipation, bloating, or nausea. 1
• For refractory IBS-D, consider 5-HT3 receptor antagonists (ondansetron 4 mg once daily, titrated to maximum 8 mg three times daily) as second-line therapy, though constipation is the most common side effect. 1
• Rifaximin (non-absorbable antibiotic) is effective as second-line therapy, though its effect on abdominal pain is limited. 1

For IBS-C (Constipation-Predominant)

• If soluble fiber fails after 4-6 weeks, start polyethylene glycol (PEG) osmotic laxative, titrated to symptom response; abdominal pain is the most common side effect. 1
• Linaclotide 290 mcg once daily on an empty stomach is the preferred second-line agent when first-line therapies fail, with high-quality evidence supporting its use for both abdominal pain and constipation. 1, 4
• Lubiprostone 8 mcg twice daily is an alternative if linaclotide is not tolerated, though nausea is more common. 1, 4
• Avoid anticholinergic antispasmodics like dicyclomine in IBS-C—they reduce intestinal motility and worsen constipation. 1

For IBS-M (Mixed Pattern) or Refractory Pain (All Subtypes)

• Tricyclic antidepressants (amitriptyline) are the most effective neuromodulators for mixed IBS, refractory abdominal pain, and global symptoms. 1, 4, 2
• Start amitriptyline 10 mg nightly and titrate slowly (by 10 mg/week) to 30-50 mg daily; continue for at least 6 months if symptomatic response occurs. 3, 1, 2
• TCAs are especially effective for patients with insomnia or diarrhea-predominant symptoms. 1, 2
• In IBS-C, use TCAs cautiously with adequate laxative therapy in place, as they may worsen constipation through anticholinergic effects. 1
• Selective serotonin reuptake inhibitors (SSRIs) may be used when TCAs are not tolerated or for IBS-C, but the supporting evidence is weaker—pooled data from five RCTs showed no significant improvement in global relief or abdominal pain. 1, 4

Probiotics: Trial for 12 Weeks

• Offer a 12-week trial of probiotics for global symptoms, bloating, and abdominal pain; discontinue if no improvement, as no single strain has demonstrated superior efficacy. 1, 2

Psychological Therapies: For Persistent Symptoms After 12 Months

• Consider IBS-specific cognitive-behavioral therapy (CBT) or gut-directed hypnotherapy when symptoms persist despite 12 months of pharmacological treatment. 3, 1, 2
• These brain-gut behavior therapies are specifically designed for IBS and differ from psychological therapies that target depression and anxiety alone. 1
• Gut-directed hypnotherapy is particularly effective in younger patients without severe psychopathology. 1, 2
• Biofeedback therapy is indicated for patients with coexisting defecatory disorders or fecal incontinence. 2

Treatment Monitoring and Adjustment

• Review treatment efficacy after 3 months and discontinue ineffective medications. 3, 1, 2
• If TCAs are effective, continue for at least 6 months before considering discontinuation. 3, 1

Critical Pitfalls to Avoid

• Do not pursue extensive diagnostic testing in patients <45 years without alarm features (unintentional weight loss ≥5%, rectal bleeding, anemia, fever, nocturnal symptoms, family history of colorectal cancer or IBD)—this reinforces illness anxiety without benefit. 1, 2
• Do not use insoluble fiber (wheat bran) in any IBS subtype—it consistently worsens bloating and overall symptom burden. 1, 2
• Do not order IgG-based food allergy panels—true IgE-mediated food allergy is rare in IBS and such tests lack validity. 1, 2
• Do not prescribe anticholinergic antispasmodics (dicyclomine) for IBS-C—they worsen constipation. 1
• Avoid long-term opioid use for chronic abdominal pain due to risks of dependence and complications. 1

When to Refer to Gastroenterology

• Refer when diagnostic uncertainty persists, alarm features are present, symptoms are severe or refractory after 12 weeks of first-line therapies, or a supervised low-FODMAP diet is needed. 1, 2