First-Line Treatment for IBS
Begin with lifestyle modifications and simple dietary advice, followed by soluble fiber (ispaghula/psyllium) at 3-4 g/day as the cornerstone pharmacological first-line treatment, combined with symptom-specific therapies: antispasmodics for pain, loperamide for diarrhea, or osmotic laxatives for constipation. 1, 2
Foundation: Lifestyle and Basic Dietary Interventions
All patients must be advised to engage in regular physical exercise, as this improves global IBS symptoms and should form the foundation of treatment 1, 2. The benefits persist for up to 5 years in clinical trials 1.
Provide first-line dietary advice focusing on:
- Regular meal patterns and adequate hydration 2
- Limiting caffeine, alcohol, and gas-producing foods 2
- Completely avoid insoluble fiber (wheat bran, corn fiber) as it consistently worsens symptoms, particularly bloating 1, 2, 3
First-Line Pharmacological Treatment
For Global Symptoms and Abdominal Pain
Start soluble fiber supplementation with ispaghula (psyllium) at 3-4 g/day, building up gradually to avoid bloating and gas 1, 2, 3. This has strong evidence for effectiveness in both global symptoms and abdominal pain 1. Soluble fiber shows significant improvement (relative risk 1.55) compared to placebo, while insoluble fiber may worsen outcomes 3.
Antispasmodics are effective for abdominal pain and global symptoms 1, 2. Dicyclomine is FDA-approved for IBS, with 82% of patients showing favorable response at 160 mg daily (40 mg four times daily) compared to 55% with placebo 4. However, anticholinergic side effects (dry mouth, visual disturbance, dizziness) commonly limit tolerability 1, 2.
Peppermint oil is an effective first-line antispasmodic option for bloating and pain with fewer side effects 2.
For IBS with Diarrhea (IBS-D)
Loperamide 2-4 mg up to four times daily reduces stool frequency, urgency, and fecal soiling 2. However, it does not improve abdominal pain 5, 6. Titrate the dose carefully to avoid abdominal pain, bloating, nausea, and constipation, which are common side effects 1, 2.
For IBS with Constipation (IBS-C)
Begin with soluble fiber (ispaghula) at 3-4 g/day, increasing gradually 1, 2. If fiber fails after 4-6 weeks, add polyethylene glycol (osmotic laxative), titrating the dose according to symptoms 2.
Probiotics as First-Line Option
A 12-week trial of probiotics may be effective for global symptoms and abdominal pain 1, 2. However, no specific species or strain can be recommended based on current evidence 1, 2. Discontinue if no improvement occurs after 12 weeks 1, 2.
Second-Line Dietary Therapy
A low-FODMAP diet is effective for global symptoms and abdominal pain when first-line measures fail 1, 2. However, implementation must be supervised by a trained dietitian with planned reintroduction of foods according to tolerance 1, 2. The quality of evidence is very low, and the diet is more restrictive and difficult to implement 1.
Do not recommend gluten-free diets unless celiac disease has been confirmed 1, 2.
Never use IgG antibody-based food elimination diets as they lack evidence and may lead to unnecessary dietary restrictions 1, 2.
Critical Pitfalls to Avoid
- Never start with insoluble fiber (wheat bran) as it will worsen symptoms, particularly bloating 1, 2, 3
- Do not promise complete symptom resolution; the goal is symptom relief and improved quality of life 2
- Avoid extensive investigations once IBS is diagnosed based on symptom criteria in the absence of alarm features 2
- Review efficacy after 3 months of treatment and discontinue if no response 1
When to Escalate to Second-Line Treatment
If symptoms persist after 3 months of first-line treatment, initiate tricyclic antidepressants (TCAs) as gut-brain neuromodulators 1, 2. Start with amitriptyline 10 mg once daily at bedtime, titrating slowly (by 10 mg/week) to a maximum of 30-50 mg daily 1, 2. TCAs have strong evidence (moderate quality) for effectiveness in global symptoms and abdominal pain 1.
Provide careful explanation that TCAs are used as gut-brain neuromodulators, not for depression, and counsel about side effects including dry mouth, drowsiness, and constipation 2.
SSRIs are effective alternatives when TCAs are not tolerated, particularly if TCAs worsen constipation in IBS-C patients 1, 2.
When to Refer to Gastroenterology
Refer when there is diagnostic doubt, severe symptoms, or symptoms refractory to first-line treatments after 12 weeks 1, 2. Consider IBS-specific cognitive behavioral therapy or gut-directed hypnotherapy when symptoms persist despite 12 months of pharmacological treatment 1, 2.