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Oral rehydration solutions

Oral rehydration solutions (ORS) are simple mixtures of water, glucose and electrolytes used to replace fluid and electrolytes lost through acute diarrhoea, vomiting and excessive sweating. The WHO/UNICEF reduced-osmolarity formula is the global reference.

What ORS are

Oral rehydration solutions are pre-formulated combinations of sodium chloride, potassium chloride, a citrate or bicarbonate buffer, and glucose, reconstituted with potable water before use. The formulation exploits the sodium-glucose co-transport mechanism in the small intestine, which allows continued absorption of fluid and sodium even in conditions where intestinal fluid losses are increased. The WHO/UNICEF "reduced-osmolarity" formula, adopted in 2002, has a total osmolarity of around 245 mOsm/L, lower than earlier ORS formulations; it is currently the standard reference formula recommended by WHO and UNICEF.

Regulatory classification in the EU

ORS sit at the boundary between several regulatory regimes:

• Medicinal products — many ORS marketed in EU countries are authorised as medicinal products and bear a national or central marketing authorisation. Their dispensation is reserved to the channels permitted for medicines under national law (pharmacy in all Member States; pharmacy plus parafarmacia / local de venda in Italy and Portugal).
• Foods for special medical purposes (FSMP) — some ORS are placed on the market as foods for special medical purposes under Regulation (EU) No 609/2013, with the labelling, composition and notification rules attached to that regime.
• Foodstuffs / "sports drinks" with electrolytes are not ORS in the medical or FSMP sense and do not meet the WHO/UNICEF composition. They should not be conflated with rehydration solutions.

Where they are sold

The sale channel for any specific ORS product depends on its regulatory classification under national law:

• An ORS product authorised as a medicinal product may be sold only in a pharmacy (in France, Spain, Belgium) or in a pharmacy or parafarmacia / local de venda (in Italy and Portugal, where the latter has a pharmacist on premises and the product is classified as non-prescription).
• An ORS product placed on the market as a food for special medical purposes can typically be sold in parapharmacy retail formats under the relevant FSMP rules; supply is to be used under medical supervision per the FSMP regime.

Intended use

ORS are intended to replace fluid and electrolyte losses. They do not, by themselves, treat the underlying cause of diarrhoea or vomiting. Decisions about whether and how to use ORS in a specific situation — particularly in young children, infants, the elderly and people with underlying chronic conditions — are clinical decisions and require the advice of a pharmacist or a physician. This site does not provide diagnostic, dosing or treatment guidance.

Practical labelling considerations

An ORS package, in any regulatory class, will indicate the intended use, the reconstitution instructions, the composition (typically listing the per-litre concentrations of sodium, potassium, chloride, citrate/bicarbonate and glucose), and the population for whom the product is suitable. Reconstitution with the volume of water indicated is essential to delivering the intended osmolarity and electrolyte concentrations; reconstitution with the wrong volume changes the product and is unsafe.

Last reviewed: May 2026.