The HS medical abbreviation most often means at bedtime: a medicine marked HS is taken once, just before the person goes to sleep. It comes from the Latin hora somni, "hour of sleep," and is written HS, hs or h.s.
The same two letters can also mean half-strength, as in a diluted solution or feeding. Because one meaning can be read as the other, the Institute for Safe Medication Practices steers bedtime orders toward QHS or qhs instead of HS, and many prescribers spell out half-strength in full. Outside medication orders, HS is also shorthand in dermatology for a skin condition. This page sorts out the meanings, shows HS in sample lines and explains how it relates to QHS and ACHS.
At a glance
Stands for
At bedtime (hour of sleep); also half-strengthLatin origin
Hora somni, hour of sleepWritten as
HS, hs, h.s.Safety status
Ambiguous; ISMP advises QHS or qhs for bedtime insteadSafer to write
QHS or qhs for bedtime; half-strength in fullOther meanings
Hidradenitis suppurativa, a chronic skin condition, in dermatology notesRelated terms
QHS (every night at bedtime), ACHS (before meals and at bedtime)
What the HS medical abbreviation means for timing
As a timing term, HS ties a dose to sleep rather than to a clock. If someone goes to bed at 10 p.m. one night and midnight the next, the HS dose moves with them. In hospitals, the bedtime medication pass happens at a standard hour, often around 21:00 or 22:00, chosen by the unit.
Medicines commonly ordered at bedtime include those that cause drowsiness, some cholesterol medicines, certain laxatives and some eye ointments that blur vision. Taking them at night either uses the drowsiness or keeps the side effect out of the way during the day.
The two meanings and why they collide
HS has two very different jobs on medication orders, and that is the root of the safety concern.
| Meaning | Example | What can go wrong |
|---|---|---|
| At bedtime | Melatonin 3 mg PO HS | Read as half-strength, so the wrong product or dose is prepared |
| Half-strength | Hydrogen peroxide HS for wound cleansing | Read as bedtime, so a full-strength product is given once at night |
Either misreading leads to the wrong preparation or wrong timing. For a bedtime dose ISMP advises QHS or qhs, half-strength is clearest written as a word, and many order systems print both in full automatically.
HS in a real order and a nurse's note
Medication order: "Trazodone 50 mg PO HS PRN sleep." This reads as one tablet swallowed at bedtime, but only when the patient needs help sleeping. The PRN makes the dose optional, and HS fixes when it may be given.
In a nursing note you might see "HS care given," which refers to the routine care offered at bedtime, such as mouth care, toileting and settling the patient for the night. "HS snack" is the small bedtime snack offered to some patients, for example people with diabetes. These uses all follow the bedtime meaning.
HS versus QHS and ACHS
HS on its own simply means at bedtime. QHS adds the Latin quaque, each, and means every night at bedtime. In practice, both describe a nightly dose for an ongoing medicine, though QHS states the every night part outright. QHS or qhs is the form ISMP now recommends for bedtime; only the mixed case Qhs is flagged, because it can be misread as qhr, every hour.
ACHS combines AC, before meals, with HS. It is the usual pattern for blood sugar checks: before breakfast, lunch and dinner, and again at bedtime. Each of these can be written out in plain words to remove any doubt.
HS outside of medication orders
In dermatology and primary care notes, HS is widely used for hidradenitis suppurativa, a long term inflammatory skin condition that causes painful lumps in areas such as the armpits and groin. A problem list entry like "HS, bilateral axillae, flaring" has nothing to do with bedtime.
The setting tells you which meaning applies. In a medication line next to a dose and route, HS is about timing or strength. In a diagnosis list or skin exam, it usually refers to the condition. If you cannot tell, ask whoever wrote it.
At bedtime medical abbreviation: what students should write
Nursing, pharmacy and scribe students will still read HS in older orders and in everyday speech, so they need to recognize it. When writing, the safer habit is QHS or qhs, the form ISMP advises, or nightly at bedtime spelled out. If you transcribe an order that says HS and the meaning is not obvious from context, clarify it before acting.
The prescription and dosing hub groups HS with other timing terms and with shorthand that ISMP does list as error-prone.
This page explains how the abbreviation is used in general. The best time of day for your own medicine, and whether a product should be diluted, are questions for your pharmacist or prescriber.
Frequently asked questions
What does HS mean on a prescription?
In a medication order, HS usually means at bedtime, from the Latin hora somni. Pharmacy labels normally print the plain words at bedtime.
Is HS on the do-not-use list?
No. The Joint Commission does not bar HS, and it has no row of its own on the ISMP error-prone list. ISMP does advise writing QHS or qhs for bedtime instead of HS, since HS can also mean half-strength. Writing half-strength as a word removes the other doubt.
What is the medical abbreviation for bedtime?
The preferred bedtime form from ISMP is QHS or qhs. HS is the older form, and many facilities simply write bedtime or nightly at bedtime in words.
What does PO HS mean?
PO HS means by mouth at bedtime. The medicine is swallowed shortly before the person goes to sleep.
What does HS mean in dermatology?
In skin care notes, HS usually stands for hidradenitis suppurativa, a chronic inflammatory skin condition. It is unrelated to the bedtime meaning.