2 Sig Codes and Directions

What a Sig communicates

A prescription’s Sig gives directions for using a medication. A complete direction should make clear what amount to use, how to use it, when or how often to use it, and any conditions or limits that apply. It may also specify duration or an indication, such as the reason for taking a medicine as needed.

Sig codes are shorthand conventions, not a universal code. Meanings can vary by organization or context, so use only abbreviations recognized by the applicable workplace standard. Do not guess when a code or direction is unclear; patient-facing directions should use clear, plain language.

Common codes and plain-language wording

These common conventions should be confirmed in context and used according to local policy:

• PO: by mouth; write “Take by mouth.”

• BID: twice daily; write “Take two times a day.”

• TID: three times daily; write “Take three times a day.”

• QID: four times daily; write “Take four times a day.”

• PRN: as needed; state the reason and any interval or maximum when specified.

• HS: at bedtime; write “Take at bedtime.”

• AC: before meals; write “Take before meals.”

• PC: after meals; write “Take after meals.”

• SL: sublingually; write “Place under the tongue.”

• TOP: topically; write “Apply to the skin.”

For example, Take 1 tablet PO BID becomes “Take 1 tablet by mouth two times a day.” This preserves the dose, route, and frequency without adding a specific clock schedule that was not written.

Check timing, route, and frequency

Check timing, route, and frequency separately when interpreting a Sig.

• Timing: Identify any time anchor or relationship to food, sleep, or another event. “At bedtime” and “every 8 hours” describe different timing instructions. Do not invent a schedule when the prescription does not specify one.

• Route: Check how the medication is used, such as by mouth, on the skin, in the eye, or by inhalation. The route must fit the dosage form. If it is missing, conflicting, or implausible, seek clarification rather than infer it.

• Frequency: Determine how often a dose is taken and whether use is scheduled or conditional. “Twice daily” means two doses per day, but does not necessarily mean exactly every 12 hours; “every 12 hours” specifies an interval. “As needed” is conditional, not a scheduled frequency. Preserve any stated minimum interval, reason, and maximum dose.

For example, 1 tablet PO q6h PRN pain can be written as “Take 1 tablet by mouth every 6 hours as needed for pain.” Keep the as-needed condition; do not turn it into a fixed schedule. If a necessary limit is not stated or an important question remains unresolved, refer the direction for clarification.

Avoid error-prone shorthand

Some abbreviations and dose formats are easily misread. The Joint Commission’s prohibited list for covered medication-related documentation includes U (unit), IU, QD (daily), QOD (every other day), a trailing zero such as 1.0 mg, and a missing leading zero such as .5 mg. Prefer writing “unit,” “International Unit,” “daily,” and “every other day” in full; write 1 mg and 0.5 mg.

ISMP also identifies additional error-prone abbreviations and recommends spelling out intended directions where confusion is possible. The safest translation preserves the prescriber’s meaning without silently resolving ambiguity. If the route, timing, frequency, or meaning of a code is uncertain—or if two parts of the direction conflict—pause and obtain clarification through the appropriate professional process.