Oral rehydration salts

Also called oral rehydration solution or ORS

Key points about rehydration salts

  • Rehydration salts are used to replace salts and water that the body loses when you are dehydrated.
  • Rehydration salts are also called oral rehydration solution or ORS.
  • Find out how to use them safely and the possible side effects.
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  • Certain types of salts (sodium, chloride, potassium) are needed by your body for many processes, eg, to regulate water in and around cells, for brain function, to aid digestion and to regulate blood pressure. So it is important to replace them if you have become dehydrated.  
  • Oral rehydration salts (ORS) are a mixture of electrolytes (salts) and carbohydrates (in the form of sugar) dissolved in water. They are used to replace salts and water that the body loses when you have dehydration caused by gastroenteritis, diarrhoea or vomiting.
  • Unlike other fluids you might drink to replace what you have lost, the proportion of salts and sugar in an ORS matches what your body needs to recover.
  • Commercially-available ORS products like drinks, ice blocks, sachets or effervescent tablets for making solutions can be bought from pharmacies. They are often available in different flavours.     
  • Home-made salt/sugar mixtures are used in developing countries if rehydration drinks are not available, but they have to be made carefully as too much salt can be dangerous. 

Note: Studies have found that for children aged 2 years or older, who are only a little dehydrated, diluted (half strength) apple juice is a good alternative to oral rehydration salts. Apple juice is more acceptable to children/tamariki, meaning that they are more likely to drink it and not need other treatment. 

Oral rehydration salts are also called

  • Electral®
  • Enerlyte®
  • Gastrolyte®
  • Hydralyte®
  • Pedialyte®

The usual dose of oral rehydration salts depends on your age and how severe your dehydration is. The following is a guide:

  • Child aged 1 month to 1 year: 1–1½ times the usual feed amount.
  • Child aged 1 to 12 years: 200 mL (about 1 cup) after every loose bowel motion (poo).
  • Child aged 12 years and over and adults: 200–400 mL ( about 1–2 cups) after every loose bowel motion.

Your health provider or the product leaflet will tell you how much ORS to take, how often to take it and any special instructions.

  • If you have sachets of powder or effervescent tablets that you need to mix with water, follow the instructions on the packaging for preparing the oral rehydration salts. Never take it without mixing it with water first.
  • Use fresh drinking water to mix with the contents of the sachet. For pepi/infants, use boiled and cooled water before mixing with the contents of the sachet.
  • Do not boil the ORS solution after mixing.
  • Some brands of ORS (such as Pedialyte) must be used within 1 hour of mixing. Any unused solution (ORS mixed with water) should be thrown away unless you store it in a refrigerator where it may be kept for up to 24 hours.

If you (or your child) are unable to drink the full dose needed all at one go, try drinking it in small sips over a longer time period. It may help to use a straw or to chill the solution.

  • If your child is sick less than 30 minutes after drinking the oral rehydration salts, give them another dose.
  • If your child is sick more than 30 minutes after drinking the oral rehydration salts, you do not need to give them again until they have their next runny poo.
  • Oral rehydration salts should start working quickly and dehydration usually gets better within 3–4 hours.

You will not harm your child by giving too much of the oral rehydration salt solution, so if you are not sure how much your child has kept down because they are being sick, it is better to give more rather than less of the oral rehydration salts.

  • You should not use oral rehydration salts to treat diarrhoea for more than 2–3 days unless your doctor has told you to.
  • You should only use water to mix with the oral rehydration salts; do not use milk or juice and never add extra sugar or salt. This is because the rehydration salts contain the right mix of sugar and salts to help the body best.
  • You must be careful to use the right amount of water to make up the medicine, as too much or too little can mean the salts in your child’s body are not properly balanced.
  • Oral rehydration salts are safe and do not usually have side effects. 
  • You can take other medicines at the same time as oral rehydration salts.
  • Avoid fizzy drinks, undiluted juices, tea, coffee and sports drinks because their high sugar content can make you more dehydrated.

The following links provide further information on oral rehydration salts.

Oral rehydration salts(external link) Medicines for Children, UK


5 questions to ask about your medications(external link) Health Quality and Safety Commission, NZ, 2019 English(external link), te reo Māori(external link)


  1. Oral rehydration salts(external link) NZ Formulary
  2. Gastrolyte (external link)Product Datasheet
  3. Hydralyte(external link) Hydralyte.com.au
  4. Pedialyte(external link) Pedialyte.com
  5. Freedman SB, Willan AR, Boutis K, et al. Effect of dilute apple juice and preferred fluids vs electrolyte maintenance solution on treatment failure among children with mild gastroenteritis – a randomized clinical trial(external link) JAMA. 2016;315:1966-1974.
  6. Moretti ME, Ungar WJ, Freedman SB, et al. Cost-effectiveness of preferred fluids versus electrolytes in pediatric gastroenteritis(external link) Can J Emerg Med 2021;23,:646–654.

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Reviewed by: Maya Patel, MPharm PGDipClinPharm, Auckland

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