Per os (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 (and grammatically incorrectly; os is a neuter noun of the 3rd declension and thus the accusative is the same as the nominative) rendered per orem, which is sometimes corrupted to per oram.

[edit] Pronunciation

• British: pər'əoυs
• U.S.: pər'oυs

[edit] See also

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

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