Glossary
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.
TID means three times a day, from the Latin ter in die ("three times in a day"). In a hospital the doses are usually given at set times that cluster in the waking day, which is exactly why TID and Q8H are not interchangeable even though both are three doses.
That difference changes the arithmetic a technician does all day. For 30 days at one tablet per dose, TID is 90 tablets, where BID is 60 and QID is 120 — and the days supply moves with it. A prescription written 1 tab PO TID, #90 is a 30-day supply; the same quantity written Q8H is also a 30-day supply, but the label directions are not the same sentence and the patient will not take them the same way. Convert the sig to a per-day amount before anything else, and the count, the days supply and the date the refill is due all follow.
TID is not on the Joint Commission's "Do Not Use" List, but it shares the family's hazard: TID and BID are one letter apart in handwriting, and the classic harm is a drug given three times a day when the order said two. Expanding the sig on the label — three times a day — is what makes the difference visible at the point the patient reads it.
Taught in
Related terms
- 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.
- 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.
- 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".
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)