Oral administration (per os) is a route of administration where a substance is taken through the mouth. Many medications are taken orally because they are intended to have a systemic effect, reaching different parts of the body via the bloodstream, for example.


Per os (/ˌpɜrˈoʊs/; P.O.) is an adverbial phrase meaning literally from Latin "by mouth" or "by way of the mouth." The expression is used in medicine to describe a treatment that is taken orally. The abbreviated P.O. is often used on medical prescriptions. P.O. is also occasionally rendered per orem, which is sometimes corrupted to per oram. These are grammatically incorrect; os is a neuter noun of the 3rd declension and thus the accusative is the same as the nominative.


Oral administration is a part of enteral administration, which also includes

  • buccal (dissolved inside the cheek)
  • sublabial (dissolved under the lip) and
  • sublingual administration (dissolved under the tongue). Note that due to rapid absorption many consider SL a parenteral route.

Enteral medications come in various forms, including:

  • tablets to swallow, chew or dissolve in water or under the tongue
  • capsules and chewable capsules (with a coating that dissolves in the stomach or bowel to release the medication there)
  • time-release or sustained-release tablets and capsules (which release the medication gradually)
  • powders or granules
  • teas
  • drops
  • liquid medications or syrups.

Facilitating methods

Concomitant ingestion of water facilitates in swallowing tablets and capsules. If the substance has disagreeable taste, addition of a flavor may facilitate ingestion. Substances that are harmful to the teeth are preferably given through a straw.

See also

  • Nil per os
  • List of Latin phrases
  • Medical prescription
  • List of abbreviations used in medical prescriptions


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