What does OD mean on a prescription?
OD has two meanings, which is why it is unsafe. In eye prescriptions OD means the right eye (oculus dexter). In UK and some other prescribing it is used for once daily.
- Means:
- right eye — or once daily, depending on country
- From:
- oculus dexter / omni die
- Type:
- How often
- Also written:
- od, o.d., OD
What it means in practice
This genuine ambiguity is the whole point of the entry. An eye-drop prescription reading “1 drop OD” could mean one drop into the right eye, or one drop daily into both. ISMP therefore recommends writing “right eye” and “daily” in words and never using OD for a frequency.
Example on a prescription
Latanoprost 0.005% 1 drop OD QHS
In an eye context this reads: one drop into the right eye each night at bedtime. If the label is not explicit, ask the pharmacist which eye and how often.
Commonly confused with
- OSOS is oculus sinister, the left eye.
- OUOU is oculus uterque, both eyes.
- QDQD is the Latin abbreviation for once a day. OD is often used the same way outside the US, which is the source of the confusion.
Frequently asked questions
Does OD mean once daily or right eye?
Both, depending on context. In ophthalmology OD is the right eye. In UK-style prescribing it is used for once daily. Safety guidance is to spell out whichever you mean.
What is the difference between OD, OS and OU?
OD is the right eye, OS the left eye, OU both eyes. They come from oculus dexter, sinister and uterque.
Related abbreviations
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This page explains prescription notation for general information. It is not medical advice and does not replace your prescriber or pharmacist. If a label is unclear or differs from what you were told, check with your pharmacy before taking the medicine.