What does "PO" stand for on a prescription?

On a prescription, “PO” stands for “by mouth,” meaning the medicine should be taken orally.

PO comes from the Latin phrase per os, literally “through the mouth.” It describes a route of administration for tablets, capsules, liquids, and other medicines swallowed or otherwise delivered through the mouth. A prescription marked PO generally tells the patient or healthcare professional that the drug is intended for oral administration rather than injection, inhalation, or application to the skin.

The abbreviation appears in medical notes, medication orders, and prescription directions, although many modern safety systems prefer writing “oral” or “by mouth” in full. Abbreviations can be misread, especially when handwriting is unclear or when a similar-looking abbreviation has a different meaning. Patients should ask a pharmacist whenever a direction is uncertain.

PO does not mean that every medicine is swallowed in exactly the same way. Some oral medicines are chewed, dissolved, or released gradually, and instructions such as “with food,” “on an empty stomach,” or “do not crush” still matter. PO is also different from sublingual or buccal administration, in which medicine is placed under the tongue or inside the cheek.