Below is a concise “field manual” you can keep handy. It explains (1) why diarrhea happens and (2) what to do when it’s severe, step by step.
(Medical information evolves; the citations show current consensus and the most recent large reviews. Always involve a clinician if any red-flag sign appears.)
1 Why we get diarrhea – the four main mechanisms
| Mechanism | What’s going on | Typical examples |
| Osmotic | Un-absorbed molecules pull water into the gut | Lactose/sorbitol intolerance, some laxatives |
| Secretory | Gut cells actively pump sodium & chloride → water follows | Cholera, ETEC “travellers’ diarrhea”, certain hormones/drugs |
| Inflammatory / Exudative | Mucosal injury leaks protein, blood & fluid | Shigella, Salmonella, ulcerative colitis |
| Altered motility | Food races through before water can be re-absorbed | Irritable-bowel syndrome, hyperthyroidism |
Most acute, watery episodes are infectious; chronic (>4 weeks) demands a work-up for malabsorption, endocrine disease, medications, etc.
2 When is it “severe”?
Any of these ⇒ go straight to a clinician or emergency department.
3 Treatment playbook
| Priority | What to do | Practical details & doses | Evidence / notes |
| Re-hydrate first, fast | WHO low-osmolar ORS (1 L water + 6 tsp sugar + ½ tsp salt) or commercial sachet | Adults ≈ 200–400 mL after each loose stool; kids 10 mL/kg | ORS alone prevents ≈ 90 % of cholera deaths |
| IV Ringer’s lactate / normal saline | In hospital for severe dehydration, shock | ||
| Replace electrolytes & micronutrients | Zinc 20 mg daily for 10–14 d (children ≥ 6 mo); 10 mg if <6 mo | Shortens episode by ~½ day and lowers 2-month relapse risk | |
| Keep eating | Resume normal diet early; use easily digested starches (rice, potatoes, bananas, toast, oatmeal) + lean protein | Avoid high-fat, very sugary drinks, alcohol, caffeine; consider temporary lactose restriction | |
| Symptom relief (adults only, afebrile, no blood) | Loperamide 4 mg, then 2 mg after each loose stool (max 8 mg OTC / 16 mg Rx per day) | Never use if bloody stool, high fever, C. difficile risk, or in children | |
| Bismuth subsalicylate 524 mg every 30–60 min (≤ 8 doses/24 h) | Adds mild antimicrobial & anti-secretory effect; avoid in aspirin allergy, kids with viral illness | ||
| Racecadotril 100 mg TID (where available) | Decreases stool volume; safe in children & adults | ||
| Antibiotics – only for specific scenarios | – Traveller’s diarrhea with moderate/severe symptoms or blood/fever – Culture-proven bacterial dysentery – Cholera – Immunocompromised host | Azithromycin 1 g single dose or 500 mg daily × 3 d (first-line worldwide)Alternatives: Rifaximin 200 mg TID × 3 d (non-invasive), Ciprofloxacin 500 mg BID × 3 d where resistance low | Empiric azithromycin remains first-line because of rising fluoroquinolone resistance |
| Probiotics (optional) | Lactobacillus rhamnosus GG or Saccharomyces boulardii | May shorten illness by ~1 day; avoid if severely immunocompromised |
4 When to seek urgent help
| Symptom | Why it matters |
| No urine for ≥8 h, sunken eyes, listlessness | Severe dehydration – IV fluids needed |
| Blood, mucus, or tarry black stool | Possible dysentery, IBD flare, or upper-GI bleed |
| High fever, shaking chills | Invasive bacterial infection or sepsis risk |
| Severe abdominal pain or distension | Toxic megacolon, perforation |
| Recent antibiotic course | Danger of C. difficile colitis |
| Diarrhea >48 h in infants / >72 h in adults despite ORS | Needs evaluation & possible labs |
5 Staying out of trouble next time
Bottom line
Diarrhea kills mainly through dehydration, so every treatment plan starts with prompt, adequate oral (or IV) re-hydration, then targets the cause or the worst symptoms. Most episodes settle in ≤ 3 days with ORS, zinc (for kids), and careful diet; medicines have supporting roles and antibiotics are selective tools – not defaults.
This guidance is for education, not a substitute for individualized medical care. If any red-flag feature emerges, contact a healthcare professional immediately.