Glossary
QID
QID means four times a day, from the Latin quater in die. It is the abbreviation most often misread as QD, and one tablet four times a day is the classic fourfold-overdose signature.
QID means four times a day, from the Latin quater in die. 1 tab PO QID, #120 is one tablet by mouth four times a day, 120 tablets, a 30-day supply.
QID is on this list because of the neighbor it is confused with. QD (once a day) and QID (four times a day) differ by a single letter, and the Joint Commission's Official "Do Not Use" List bans QD for exactly that reason — the fix is to write daily, which removes the pair from the vocabulary altogether. Removing QD is also what protects QID: a prescriber who writes out 1 tab daily cannot be misread as four times a day.
Four times a day is a demanding schedule, and that is a counseling point as much as an arithmetic one. In practice the doses land roughly at waking, midday, evening and bedtime — closer to six hours apart than to a true Q6H, and nowhere near a clock. A patient who cannot manage four doses a day is a patient the pharmacist may need to talk to the prescriber about, and a technician who recognizes the schedule is the one who raises it.
On a calculation question, QID is a per-day factor of 4: quantity ÷ 4 gives the days supply, and days × 4 gives the tablet count.
Taught in
Related terms
- QD — QD means once a day, from the Latin quaque die. It is on the Joint Commission's Do-Not-Use List because QD and QID are misread for each other, so the order is written out as "daily".
- TID — TID means three times a day, from the Latin ter in die. It is three doses spread across the waking day, not a strict every-8-hours order — that one is written Q8H.
- BID — BID means twice a day, from the Latin bis in die. It is two doses in a day rather than a strict every-12-hours schedule — the fixed-interval order is written Q12H.
Source: PTCB — PTCE Content Outline, effective January 6, 2026 (Domain 4 / KA 4.1, "Interpret prescription and medication orders … sig codes, abbreviations, medical terminology and symbols, and days supply", quoted verbatim); The Joint Commission, Official "Do Not Use" List (NPSG.03.05.01 — the minimum list an accredited organization must adopt, read in full); ISMP, List of Error-Prone Abbreviations, Symbols, and Dose Designations (the labels, symbols and abbreviations ISMP asks prescribers to write out) (outline accessed 2026-10-03, verbatim; the Joint Commission and ISMP lists read from their own fact-sheet and recommendation pages 2026-10-06 — each is revised on its own schedule; the definitions here restate this course's own order-interpretation-and-sig guide, which is the page whose sources back every definition above)