Open Source Apothecary At Home / Digestion

Acute diarrhoea: rehydration first, everything else second

The treatment that saves lives is a measured salt-and-sugar solution. No herb in this handbook comes close.

remedy

Acute diarrhoea kills through dehydration and electrolyte loss, and the intervention with the largest effect on mortality is oral rehydration solution — water, salt and sugar in the right proportions. Everything else is secondary to that.

Why the sugar matters. Sodium is absorbed from the gut coupled to glucose via the SGLT1 transporter. Water follows the sodium. A solution with salt but no sugar, or sugar but no salt, is absorbed poorly; the combination is what makes oral rehydration work, and it is why a sports drink (too much sugar, too little salt) and plain water are both inferior to the proper mix. Do not "improve" the recipe by adding more sugar.

Zinc has randomised trial evidence in acute diarrhoea in children in low-income settings, reducing duration and stool volume, and it is standard WHO practice there. Whether it helps in a well-nourished child in a high-income setting is less clear.

Probiotics have a modest effect on duration of infectious diarrhoea in pooled analyses, with strain-dependent results and some heterogeneity. They are not a treatment for dehydration.

What not to do. Antimotility drugs (loperamide) reduce the diarrhoea and can cause harm in invasive bacterial infection such as Shigella or Salmonella, by keeping the organism and toxin in the gut. They are the wrong choice with blood in the stool or a high fever. Antibiotics are not needed for most cases and are a decision for a clinician. And do not stop the diarrhoea before it is safe to do so in a suspected invasive infection.

Demulcents — a cold infusion of marshmallow or slippery elm, or simply oats — soothe a sore gut and are reasonable comfort measures. They are not rehydration.

What the studies found

Preparation

Oral rehydration solution — the proportions matter

• 1 litre of clean water
• 6 level teaspoons of sugar (about 20 g)
• Half a level teaspoon of salt (about 2.5 g)
• Stir until dissolved. Do not add more sugar or more salt.
• A commercial ORS sachet is more precise and is worth keeping in the house.

How to give it

• Small, frequent sips. In a child, a spoonful every 1-2 minutes.
• Aim for roughly 200 mL (a glass) after each loose stool in an adult; smaller volumes and more often in a child.
• If it is vomited, wait 10 minutes and start again more slowly. Some absorption happens even when vomiting.

Zinc (children)

• Trials used 20 mg daily for 10-14 days in children over 6 months, 10 mg under 6 months
• Only with a clinician's advice in a high-income setting

Probiotics

• Saccharomyces boulardii and Lactobacillus rhamnosus GG are the most studied
• An adjunct, not a substitute for rehydration

Demulcent

• Cold infusion of marshmallow root or slippery elm, sipped
• Plain cooked rice, oats, or broth as tolerated

Food

• Continue eating as tolerated. Starving a gut does not shorten the illness.

Cautions and interactions

• Do not use loperamide (Imodium) if there is blood in the stool or a high fever. Retaining an invasive organism and its toxin can cause serious harm.
• Do not give loperamide to a child without medical advice.
• Do not add extra sugar to ORS. Too much sugar pulls water into the gut and worsens the diarrhoea.
• Probiotics are risky in the severely unwell, immunocompromised, or critically ill — cases of fungaemia have occurred with Saccharomyces.
• Do not give honey or homemade sugar solutions to an infant under 12 months other than properly made ORS on medical advice.

When this is not a self-care problem — get help

• Signs of dehydration: no urine for 8 hours, sunken eyes, no tears when crying, a dry mouth, lethargy, or a child who is floppy — urgent care.
• Blood or mucus in the stool, a high fever, severe abdominal pain, or diarrhoea after recent antibiotics (consider C. difficile) — medical assessment.
• A baby under 6 months with diarrhoea, or any child who is drowsy, not drinking, or passing no urine — emergency care.

Known interactions

• Antimotility drugs and antibiotics: several interactions; a pharmacist is the right check.

Related

• Dehydration and heat illness
• The gut microbiome: what is actually established
• Constipation: fibre, water, and when a laxative is the wrong tool
• Fever: what it is for, and when it means something else
• Children: smaller, and different

Sources

1. Efficacy of interventions for the treatment of irritable bowel syndrome, functional abdominal pain-not otherwise specified, and abdominal migraine in children: a systematic review and network meta-analysis. The Lancet. Child & adolescent health 2025; doi:10.1016/S2352-4642(25)00058-6 PubMed 40246358
2. Zinc supplementation for acute and persistent watery diarrhoea in children: A systematic review and meta-analysis. Journal of global health 2024; doi:10.1016/S0140-6736(14)61698-6 PubMed 39641338
3. Efficacy of antimicrobial and nutraceutical treatment for canine acute diarrhoea: A systematic review and meta-analysis for European Network for Optimization of Antimicrobial Therapy (ENOVAT) guidelines. Veterinary journal (London, England : 1997) 2024; doi:10.1016/j.tvjl.2023.106054 PubMed 38049062
4. The Efficacy of Probiotics, Prebiotics, Synbiotics, and Fecal Microbiota Transplantation in Irritable Bowel Syndrome: A Systematic Review and Network Meta-Analysis. Nutrients 2024; doi:10.1136/gutjnl-2016-312513 PubMed 38999862
5. Efficacy of Probiotics in Irritable Bowel Syndrome: Systematic Review and Meta-analysis. Gastroenterology 2023; doi:10.1053/j.gastro.2023.07.018 PubMed 37541528
6. Outcome-Specific Efficacy of Different Probiotic Strains and Mixtures in Irritable Bowel Syndrome: A Systematic Review and Network Meta-Analysis. Nutrients 2023; doi:10.3389/fcimb.2022.859967 PubMed 37686889