Glossary
QHS
QHS means at bedtime, from the Latin hora somni — the hour of sleep. ISMP lists it as error-prone because HS also reads as "half strength", so the words are written out instead.
QHS means at bedtime, from the Latin hora somni, "the hour of sleep". The order 1 tab PO QHS is one tablet by mouth at bedtime.
What makes QHS a term worth knowing is the ambiguity inside the shorter spelling. HS can mean hora somni — bedtime — or it can mean half strength, and the two live in the same prescriptions: a half-strength cream and a bedtime dose are both real, and the same pair of letters can stand for either. That is why ISMP puts HS and QHS on its List of Error-Prone Abbreviations and asks for the words instead; the Joint Commission's own "Do Not Use" List does not include them, which is the distinction an exam question is usually drawing — one list is the accredited minimum, the other is the error-prone guidance.
The clinical logic behind a bedtime dose is usually side effects rather than the disease: a drug that causes drowsiness is moved to bedtime so the patient sleeps through it, and a bedtime dose is often paired with a standing order for something else during the day. Read the sig before assuming the schedule is arbitrary — the same drug is sometimes written QHS for one reason and QAM for the opposite one.
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".
- PRN — PRN means "as needed", from the Latin pro re nata. By itself it sets no schedule and no ceiling, so the sig must still state the dose, the shortest interval allowed, and the maximum in 24 hours.
- sig code — The sig is a prescription's directions, and a sig code is the shorthand written inside it — BID for twice a day, QHS for at bedtime. The pharmacy expands each code into plain English on the label.
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)