What do OU, OD and OS mean on a prescription?
OU means both eyes, OD means right eye, and OS means left eye. AU, AD and AS are the matching codes for the ears.
What it stands for
OU, OD and OS comes from the Latin oculus uterque, oculus dexter, oculus sinister, meaning each eye, right eye, left eye. It tells you which eye the drops go in.
How it looks on a real label
| Sig code | Label directions |
|---|---|
2 gtts ou bid | Instill 2 drops in both eyes twice daily |
1 gtt as tid | Instill 1 drop in left ear three times daily |
The ear codes follow the same pattern with A for auris: AU is both ears, AD is right ear, AS is left ear.
These are on the ISMP list of error-prone abbreviations, because OD and AD differ by one letter and put a medication in the wrong organ entirely. Many pharmacies now write "right eye" and "left ear" in full on the label even when the prescription used the code.
OD is also genuinely ambiguous: it means right eye in an ophthalmic sig and once daily in an oral one. Context is the only thing separating them, which is exactly why it is discouraged.
Related codes
| Code | Meaning |
|---|---|
GTT | drop |
AU | in both ears |
AD | in right ear |
AS | in left ear |
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This page is educational and is not medical advice. Always follow the directions on your own prescription and ask your pharmacist if anything is unclear.