What is the recommended management for irritable bowel syndrome (IBS), including lifestyle, dietary, and pharmacologic treatments for diarrhea‑predominant (IBS‑D), constipation‑predominant (IBS‑C), and mixed (IBS‑M) subtypes?

Management of Irritable Bowel Syndrome

Begin with lifestyle modifications and soluble fiber for all IBS patients, then escalate to symptom-directed pharmacotherapy based on the predominant bowel pattern (diarrhea, constipation, or mixed), reserving neuromodulators and psychological therapies for refractory cases after 12 months of first-line treatment.

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Initial Diagnosis and Patient Communication

• Make a positive IBS diagnosis based on abdominal pain occurring at least 1 day per week for the past 3 months, associated with altered bowel habit, in the absence of alarm features (rectal bleeding, unintentional weight loss ≥5%, anemia, fever, nocturnal symptoms, family history of colorectal cancer or inflammatory bowel disease). 1

• Order only celiac serology, complete blood count, and C-reactive protein or fecal calprotectin (in patients <45 years with diarrhea) to exclude organic disease; do not routinely test for food allergies, small intestinal bacterial overgrowth, or exocrine pancreatic insufficiency. 1, 2

• Explain to the patient that IBS is a disorder of gut-brain interaction with a benign, relapsing-remitting course that is not progressive and does not lead to cancer or inflammatory bowel disease; this reduces anxiety, improves adherence, and decreases unnecessary healthcare visits. 1, 3

• Introduce the concept of the gut-brain axis using simple language (e.g., "your gut and brain communicate constantly, and stress or certain foods can trigger symptoms"), which helps patients understand how diet, stress, and emotional responses influence their bowel function. 1, 3

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Universal First-Line Interventions (All IBS Subtypes)

Lifestyle Modifications

• Recommend regular moderate-intensity aerobic exercise to all IBS patients, as this improves global symptom scores, particularly constipation, with benefits maintained for at least five years. 4, 3

• Advise patients to limit excess caffeine, allow adequate time for regular morning defecation, and correct inappropriate self-imposed dietary restrictions (e.g., unnecessary avoidance of entire food groups). 1, 3

Dietary Interventions

• Start soluble fiber (psyllium/ispaghula) at 3–4 g daily and titrate upward gradually to minimize bloating and gas; this improves global IBS symptoms and abdominal pain across all subtypes. 1, 4, 3

• Avoid insoluble fiber such as wheat bran, as it consistently worsens bloating, abdominal pain, and overall symptom burden in all IBS subtypes. 1, 4, 3

• Do not recommend gluten-free diets unless celiac disease is confirmed by serology and biopsy, as current evidence does not support their use in IBS. 1, 4, 2

• Do not order IgG antibody-based food elimination diets, as they lack supporting evidence and may lead to unnecessary dietary restrictions. 1, 4, 3

• Consider a 12-week trial of probiotics for global symptoms and abdominal pain; discontinue if no improvement, as no specific strain has demonstrated superior efficacy. 1, 4, 3

Second-Line Dietary Therapy (If First-Line Fails After 4–6 Weeks)

• Refer to a trained dietitian for a supervised low-FODMAP diet delivered in three phases: (1) restriction for 4–6 weeks, (2) systematic re-introduction of FODMAPs according to tolerance, and (3) personalized long-term maintenance to avoid unnecessary restrictions. 1, 4, 3

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Symptom-Directed Pharmacotherapy

For Abdominal Pain and Cramping (All Subtypes)

• Prescribe antispasmodics with anticholinergic properties (dicyclomine) taken before meals as first-line therapy for meal-related abdominal pain; counsel patients about dry mouth, visual disturbances, and dizziness. 1, 4

• Use peppermint oil as an alternative antispasmodic with a more favorable side-effect profile for abdominal pain. 1, 4

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For Diarrhea-Predominant IBS (IBS-D)

First-Line Pharmacotherapy

• Prescribe loperamide 2–4 mg up to four times daily (regular dosing or prophylactically before outings) to reduce stool frequency, urgency, and fecal soiling; titrate carefully to avoid constipation, bloating, or abdominal pain. 1, 4

Second-Line Pharmacotherapy

• Add rifaximin as a second-line agent to improve overall IBS-D symptoms, though its impact on abdominal pain is modest. 1, 4

• Consider eluxadoline for patients with persistent diarrhea who have not responded to loperamide or dietary modifications. 4

• Avoid alosetron (5-HT₃ receptor antagonist) due to serious safety concerns, including the risk of ischemic colitis. 1, 4

Bile Acid Malabsorption Screening

• Test for bile acid malabsorption (SeHCAT scan or serum 7α-hydroxy-4-cholesten-3-one) in patients with nocturnal diarrhea or a history of cholecystectomy; if positive, prescribe cholestyramine. 1

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For Constipation-Predominant IBS (IBS-C)

First-Line Pharmacotherapy

• If soluble fiber fails after 4–6 weeks, add polyethylene glycol (PEG) osmotic laxative and titrate to symptom response; abdominal discomfort is the most common adverse effect. 1, 4, 3

• Re-evaluate PEG efficacy after 3 months; discontinue if meaningful improvement is not achieved. 1, 4

Second-Line Pharmacotherapy (Prescription Secretagogues)

• Prescribe linaclotide 290 µg once daily on an empty stomach (≥30 minutes before the first meal) as the preferred second-line agent after failure of first-line therapies; high-quality trials (>6,000 participants) show significant benefit for both constipation and abdominal pain. 1, 4

• Diarrhea is the most common adverse event with linaclotide; review efficacy after 3 months and discontinue if no response. 1

• Prescribe plecanatide 3 mg daily as an alternative secretagogue with efficacy comparable to linaclotide for patients who cannot tolerate or afford linaclotide. 4

• Prescribe lubiprostone 8 µg twice daily with food as a conditional third-line option for women with IBS-C; nausea occurs in ~19% versus 14% with placebo. 1, 4

Critical Pitfall: Avoid Anticholinergic Antispasmodics in IBS-C

• Do not prescribe anticholinergic antispasmodics (dicyclomine, hyoscyamine) in IBS-C, as they reduce intestinal motility and worsen constipation. 1, 4

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For Mixed IBS (IBS-M) or Refractory Abdominal Pain

Neuromodulators (Second-Line for Pain)

• Prescribe tricyclic antidepressants (amitriptyline) as the most effective second-line treatment for global symptoms and abdominal pain across all IBS subtypes; start at 10 mg nightly and titrate by 10 mg weekly to a target of 30–50 mg daily. 1, 4, 3

• Continue effective tricyclic therapy for at least 6 months before considering discontinuation if sustained symptomatic improvement is reported. 1, 4

• In IBS-C, ensure concurrent laxative therapy (PEG) is in place when prescribing tricyclics to mitigate anticholinergic-induced worsening of constipation. 1, 4

• Counsel patients about common adverse effects of amitriptyline: dry mouth, visual disturbances, and dizziness. 1, 4

• When tricyclics are not tolerated or exacerbate constipation, prescribe selective serotonin reuptake inhibitors (SSRIs) as an alternative neuromodulator, although supporting evidence is weaker. 1, 4

• Do not prescribe SSRIs solely for IBS symptom relief in IBS-D, as pooled data from five RCTs show no significant improvement in global relief or abdominal pain. 1, 4

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Psychological Therapies (Third-Line for Refractory Symptoms)

• Offer IBS-specific cognitive-behavioral therapy (CBT) and gut-directed hypnotherapy when symptoms remain refractory after at least 12 months of optimal pharmacologic management; both modalities reduce overall symptom burden. 1, 4, 3

• Prioritize psychological therapies for patients whose symptoms are stress-related, associated with anxiety or depression, or of relatively short duration. 4

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Treatment Monitoring and Reassessment

• Assess treatment efficacy at 3 months; discontinue any therapy that does not provide meaningful benefit. 1, 4, 3

• When tricyclic antidepressants are effective, maintain them for a minimum of 6 months before contemplating discontinuation. 1, 4

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Referral to Gastroenterology

• Refer to gastroenterology when diagnostic uncertainty exists, alarm features are present, symptoms are severe or refractory after 12 weeks of first-line therapy, or the patient requests specialist input. 1, 3

• Colonoscopy is reserved for patients with alarm features or for IBS-D patients with atypical risk factors (age ≥50 years, female sex, autoimmune disease, recent onset <12 months, or use of NSAIDs/PPIs) to exclude microscopic colitis. 1, 3

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Critical Pitfalls to Avoid

• Do not pursue extensive diagnostic testing in patients <45 years without alarm features, as this reinforces illness anxiety and adds unnecessary cost without benefit. 1, 3

• Do not continue docusate (Colace), as it adds no benefit to other laxative therapy and lacks efficacy for constipation. 4

• Do not prescribe opioid analgesics for chronic abdominal pain in IBS due to the high risk of dependence, opioid-induced bowel dysfunction, and other complications. 4

• Avoid extensive investigations once an IBS diagnosis is established, as unnecessary testing can reinforce illness behavior and delay appropriate treatment. 1, 4, 3