Diarrhea
Replace Fluids, Keep Eating, and Watch for Blood
General information from an emergency physician. It adds to your discharge papers and does not replace them or your own doctor. What this site is and isn’t
Key Takeaways:
- Most acute diarrhea gets better with fluids, food, and time.
- Antibiotics are usually unnecessary and can be dangerous with Shiga-toxin E. coli.
- Blood in stool, dehydration, or severe pain needs reassessment.
About Your Diagnosis & ED Workup
Most acute diarrhea is watery and caused by infection. In most U.S. adults, no specific germ is found.
Viruses damage cells that absorb food and water. Sugar left in the bowel pulls in water. New gut cells then grow and replace the damaged surface.
Most acute diarrhea does not need stool testing. Testing is more useful with blood, fever, severe illness, weak immunity, hospital exposure, or symptoms lasting at least 14 days.
First Steps & Evidence-Based Home Care
Use oral rehydration solution to replace water and salts. Sports drinks, soda, and apple juice are not equivalent.
Eat a normal diet as soon as tolerated. Fasting and the BRAT diet are not supported. Breastfed infants should keep nursing.
Wash hands with soap and water for at least 20 seconds. Alcohol gel works less well against norovirus.
Do not use loperamide for diarrhea with blood or fever. Slowing the bowel can keep invasive germs and toxins in contact with it longer.
Do not self-treat bloody diarrhea with antibiotics or anti-diarrheal medicine. With some infections, either can raise the risk of hemolytic uremic syndrome, which can injure the kidneys.
Do not give loperamide to a child under three.
Timeline & Expected Recovery Course
Most infectious diarrhea lasts 3 to 7 days. Norovirus often lasts 2 to 3 days.
Symptoms lasting 14 to 30 days are called persistent diarrhea and may need testing for other causes. Symptoms beyond 30 days are chronic.
Temporary trouble digesting lactose can follow a stomach bug because the damaged surface cells carry the needed enzyme.
Emergency Red Flags (When to Return Immediately)
Return to the emergency department for any of these. This list is not exhaustive.
- Very little or dark urine, dizziness, fainting, confusion, or a fast heartbeat.
- Bloody, black, or mucus-filled stool. Do not self-treat bloody diarrhea with antibiotics or anti-diarrheal medicine while waiting for evaluation.
- Fever above 38.5°C or severe belly pain.
- Illness lasting at least 7 days.
- Diarrhea with recent antibiotics or hospitalization, especially if worsening.
Reviewed September 3, 2026