What does Q4H mean on a prescription?
Q4H means every four hours around the clock — about six doses in 24 hours, including overnight if the order does not say “while awake”.
- Means:
- every 4 hours
- From:
- quaque 4 hora
- Type:
- How often
- Also written:
- q4h, q4°, Q4H, q 4 h
What it means in practice
The QnH family sets a strict interval rather than a count of daily doses. Q4H is used where blood levels need to stay steady, or for short-acting pain relief. Because it implies night doses, prescribers sometimes add “while awake” to limit it to waking hours.
Example on a prescription
Paracetamol 500 mg PO Q4H PRN pain, max 4 g/24h
Take 500 mg of paracetamol by mouth no more often than every four hours when you have pain, and no more than 4 g in any 24 hours.
Commonly confused with
- QIDQID is four times a day within your waking hours. Q4H is every four hours by the clock — up to six doses.
- Q6HQ6H is every six hours, four doses a day.
Worth knowing
With Q4H PRN painkillers, the interval and the 24-hour maximum both matter. Paracetamol overdose most often happens by taking correct single doses too close together.
Frequently asked questions
How many doses is Q4H in a day?
Up to six, if taken strictly every four hours over 24 hours. If the order says 'while awake' it will be fewer.
Is Q4H the same as QID?
No. QID is four doses inside your waking day. Q4H is every four hours by the clock, which can be six doses and may include overnight.
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.