Rehydration and symptom relief in diarrhoea
What helps, what harms, and how to use treatments safely
The primary goal
Prevent dehydration and electrolyte imbalance.
Diarrhoea itself is rarely dangerous. Dehydration is the main cause of complications.
Oral Rehydration Solution (ORS)
Oral Rehydration Solution (ORS) is the treatment of choice for most people with diarrhoea.
Practical ORS guidance
- Start ORS early
- Take small, frequent sips
- Continue ORS even if stools remain loose
- Combine with light food as tolerated
ORS is far more effective than plain water.
Vomiting: how to still rehydrate
Effective strategy: 5–10 mL every 2–3 minutes, gradually increase, restart after vomiting.
When intravenous (IV) fluids are needed
- Persistent vomiting preventing intake
- Moderate to severe dehydration
- Confusion or drowsiness
- Minimal or absent urine output
- Circulatory compromise
These situations require medical assessment and IV fluids.
Anti-diarrhoeal medications
Loperamide
May reduce stool frequency but must be used cautiously.
- May be used if no fever and no blood.
- Must NOT be used if fever, blood/mucus, suspected C. diff, or suspected STEC (HUS risk).
Diphenoxylate–atropine (Lomotil)
Limited role; similar cautions to loperamide; generally avoided in infectious diarrhoea.
Antiemetics (anti-nausea medication)
Antiemetics can be the key intervention that allows successful rehydration.
Ondansetron
Commonly used and effective for nausea/vomiting associated with diarrhoeal illness.
Orally disintegrating wafers (ODT / wafers)
Ondansetron orally disintegrating wafers (e.g. ZAPID and equivalent) dissolve on the tongue.
- Absorbed through the oral mucosa
- Do not rely on gut absorption
- Less likely to be vomited back up
- Often work faster and more reliably than swallowed tablets
Practical use
- Allow the wafer to dissolve fully on the tongue
- Restart ORS with small, frequent sips once nausea improves
Safety notes
- Generally well tolerated; constipation/headache can occur
- Rare QT prolongation — caution in those with risk factors
- Use in children and pregnancy should follow medical advice
Analgesics (pain relief)
- Paracetamol (acetaminophen) is preferred
- Avoid NSAIDs (e.g. ibuprofen) when dehydrated
Nutrition during diarrhoea
- Continue eating if appetite allows
- Light, bland foods are appropriate
- Avoid prolonged fasting
Common mistakes to avoid
- Drinking only water instead of ORS
- Using sports drinks as ORS substitutes
- Stopping ORS because diarrhoea continues
- Using loperamide despite fever or blood
- Delaying care when vomiting prevents intake
Key takeaway: Early, correct rehydration prevents most complications. Symptom relief should support hydration, not replace it.