What does QD mean on a prescription?
QD means once a day — a single dose every 24 hours. Because QD is easily misread, safety bodies now recommend prescriptions say “daily” instead.
- Means:
- once a day
- From:
- quaque die
- Type:
- How often
- Also written:
- qd, q.d., QD, q1d
What it means in practice
QD is Latin for quaque die, “every day”. It is one of the most frequently misread abbreviations in medicine: handwritten QD can be mistaken for QID (four times a day) if the tail of the q is read as an i, and for QOD (every other day). The Institute for Safe Medication Practices lists QD on its error-prone abbreviations list for exactly this reason, and The Joint Commission includes it on the Do Not Use list.
Example on a prescription
Lisinopril 10 mg PO QD
Take one 10 mg lisinopril tablet by mouth once a day. A modern label would print this as “take 1 tablet by mouth daily”.
Commonly confused with
- QIDQID is four times a day. This is the classic QD/QID mix-up and can mean a fourfold overdose.
- QODQOD is every other day. Confusing it with QD doubles or halves the intended dose.
- ODOD is read as once daily in some countries but means right eye (oculus dexter) in others.
Frequently asked questions
Is QD once a day or four times a day?
QD is once a day. Four times a day is QID. The two are confused often enough that both ISMP and The Joint Commission advise writing 'daily' rather than QD.
What is the difference between QD and OD?
QD is quaque die, once a day. OD is ambiguous — it is used for 'once daily' in the UK and some other countries, but in ophthalmology it means the right eye. Because of that, OD should not be used for a frequency.
Does it matter what time of day I take a QD medicine?
Consistency matters more than the specific hour. Pick a time you will remember and keep to it, unless the label or your pharmacist specifies morning or bedtime.
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.