The use of Psyllium husk (from Plantago ovata) has been reviewed as a highly effective non‑pharmacological option for managing both constipation and diarrhea. PMC
Psyllium husk’s effectiveness stems from its physicochemical properties: once the husk is mixed with water it forms a viscous gel that retains water in the intestines. This leads to softer, bulkier stool that is easier to evacuate. PMC+2Wikipedia+2 In cases of constipation — both occasional and chronic — psyllium increases stool hydration and volume, improves bowel‑movement frequency, and often performs better than a pharmacological treatment such as sodium docusate. PMC+1
Interestingly, psyllium also helps in diarrhea (acute or chronic), by absorbing excess water and increasing stool viscosity and firmness, making stools more formed rather than watery. PMC+1
Clinical trials generally use a dosage of around 10–15 grams per day, split into multiple doses (e.g. ~3.4–5 g before meals), always dissolved in ~150–200 ml liquid, followed by an extra glass of water. Gradual dose escalation is advised to reduce possible side‑effects such as bloating. PMC
Psyllium husk is generally safe and inexpensive: because its effect is mechanical (gel + water retention) rather than stimulant, it carries less risk than many laxatives. PMC+1
Nevertheless there are contraindications: psyllium should not be used by people with known allergy to psyllium, those with swallowing difficulties, mechanical obstruction of the digestive tract, or recent gastrointestinal surgery. It should also be avoided by severely malnourished individuals, people on muscle‑relaxant drugs, and infants under 3 years because of choking risk. PMC
In sum, psyllium husk stands out as a "gold standard" fiber for normalizing bowel movements. It offers a dual benefit — relieving both constipation and diarrhea — while being safe, accessible, and inexpensive. PMC+2Wikipedia+2