What is psyllium, including its mechanism, recommended adult dosing, indications, contraindications, and common side effects?

What is Psyllium?

Psyllium is a soluble, viscous dietary fiber derived from the seed husks of Plantago ovata that forms a gel when hydrated, used therapeutically to treat chronic constipation, improve glycemic control, and facilitate weight loss. 1

Mechanism of Action

Psyllium works through multiple physiological mechanisms:

• Gel formation: When mixed with water and gastrointestinal fluids, psyllium dissolves and forms a viscous gel-like substance in the stomach and intestines 1
• Increased intestinal viscosity: The gel increases chyme viscosity in the small intestine, slowing gastric emptying and nutrient absorption 2, 3
• Bulk formation: Acts as a bulk-forming agent by absorbing fluid and increasing stool mass, which stimulates peristalsis and improves bowel movements 1
• Delayed fermentation: Unlike other fibers, psyllium is not readily fermented by colonic bacteria, which reduces gas production compared to fermentable fibers 2, 3

Recommended Adult Dosing

For chronic idiopathic constipation: 10-12 g/day divided into two doses (typically 5 g twice daily), taken with at least 240-300 mL of water per dose 1, 4

For weight loss: 10-11 g/day divided into 2-3 doses, taken immediately before meals with 240-300 mL of water 5, 3

Minimum treatment duration: At least 4 weeks for constipation; 4 months for optimal weight loss benefits 5, 4

Clinical Indications

Primary Indications:

• Chronic idiopathic constipation: Psyllium is the only fiber supplement with solid evidence of efficacy, increasing spontaneous bowel movements by 2.32 per week (95% CI: 0.86-3.79) and improving global symptom relief (RR 1.86,95% CI: 1.49-2.30) 1, 4
• Pregnancy-related constipation: Safe during pregnancy due to lack of systemic absorption; improves stool viscosity and transit time 1
• Weight management: Effective for decreasing body weight (mean difference -2.1 kg), BMI (-0.8 kg/m²), and waist circumference (-2.2 cm) in overweight/obese populations 5, 3

Secondary Benefits:

• Glycemic control in metabolic syndrome and type 2 diabetes 3
• Lowering LDL cholesterol in hypercholesterolemic patients 1, 3
• Irritable bowel syndrome (improves both constipation and diarrhea) 6, 2

Contraindications

Absolute contraindications:

• Opioid-induced constipation: Psyllium may worsen symptoms; use osmotic or stimulant laxatives instead 4
• Non-ambulatory patients: Risk of intestinal obstruction due to inadequate mobility 4
• Intestinal obstruction or suspected obstruction: Bulk-forming agents can exacerbate blockage 1, 4

Relative contraindications:

• Difficulty swallowing or esophageal disorders (choking risk if not taken with adequate fluid) 1
• Dehydration or inability to maintain adequate fluid intake 1, 4

Common Side Effects

Most frequent adverse effects:

• Flatulence: The most common side effect, with a standardized mean difference of 0.80 (95% CI: 0.47-1.13) compared to placebo 1, 5
• Abdominal distension/bloating: Particularly during initial treatment; may be minimized by starting with lower doses 1, 5

Serious but rare adverse effects:

• Intestinal obstruction: Can occur if psyllium is not taken with adequate fluids (240-300 mL per dose), especially in elderly patients or with prolonged use 5, 4

Important safety note: No serious adverse events were reported in clinical trials when psyllium was used appropriately with adequate hydration 1

Clinical Pitfalls and Caveats

• Adequate hydration is critical: Each dose must be mixed with at least 240-300 mL of water to prevent intestinal obstruction 1, 5, 4
• Timing matters for weight loss: Psyllium should be taken immediately before meals to maximize viscosity effects on nutrient absorption 5, 3
• Treatment duration: Minimum 4 weeks needed to assess efficacy for constipation; premature discontinuation may lead to perceived treatment failure 4
• Not all fibers are equal: Unlike psyllium, other fibers like bran and inulin have very low or uncertain evidence for constipation treatment 1, 4
• Escalation strategy: If inadequate response after 4 weeks, escalate to osmotic laxatives (polyethylene glycol, lactulose) or stimulant laxatives rather than increasing psyllium dose indefinitely 4