GottaDose / Free tools / Prescription abbreviations

What do bid, tid and qid mean on a prescription?

Q: What does prn mean on a prescription?

It stands for pro re nata, as needed. You take the medicine when you have the symptom, not on a schedule. Labels often add a limit, such as “max 3/day”. Don't go over it.

Q: What does Sig mean?

Sig is short for the Latin signa, “label”. The text after it is what the pharmacy prints on your label: the dose, how often and for how long.

bid is twice a day, tid is three times a day and qid is four times a day. They're short for the Latin bis in die, ter in die and quater in die. Paste your label below and the decoder will spell out the rest.

Common prescription abbreviations

Most of them are Latin. Upper or lower case and the dots don't change the meaning: q.i.d., QID and qid are the same thing.

How often

Abbreviation	Latin	Meaning
`qd`	quaque die	every day (on the “Do Not Use” list, see below)
`bid`	bis in die	twice a day
`tid`	ter in die	three times a day
`qid`	quater in die	four times a day
`qod`	quaque altera die	every other day (on the “Do Not Use” list)
`q4h`, `q6h`, `q8h`	quaque … hora	every 4, 6 or 8 hours
`q4-6h`		every 4 to 6 hours
`qhs`	quaque hora somni	every night at bedtime
`prn`	pro re nata	as needed
`stat`	statim	right away
`x 7 days`, `x7d`		for 7 days

When to take it

Abbreviation	Latin	Meaning
`ac`	ante cibum	before meals
`pc`	post cibum	after meals
`hs`	hora somni	at bedtime
`qam`	quaque ante meridiem	every morning
`qpm`	quaque post meridiem	every evening
`npo`	nil per os	nothing by mouth

How to take it

Abbreviation	Latin	Meaning
`po`	per os	by mouth
`sl`	sub lingua	under the tongue
`pr`	per rectum	rectally
`top`		on the skin
`inh`		inhaled
`IM`, `IV`		into a muscle, into a vein
`SUBQ`, `subcut`		under the skin
`OD`, `OS`, `OU`	oculus dexter, sinister, uterque	right eye, left eye, both eyes
`AD`, `AS`, `AU`	auris dextra, sinistra, utraque	right ear, left ear, both ears

Forms and amounts

Abbreviation	Latin	Meaning
`tab`	tabella	tablet
`cap`	capsula	capsule
`gtt`	guttae	drops
`supp`	suppositorium	suppository
`susp`, `sol`		suspension, solution
`mg`, `mcg`		milligram, microgram
`mL`		milliliter
`tsp`, `tbsp`		teaspoon (5 mL), tablespoon (15 mL)
`ER`, `XR`, `SR`		extended or sustained release

On the prescription itself

Abbreviation	Latin	Meaning
`Rx`	recipe	take; marks the start of a prescription
`Sig`	signa	label; the directions follow
`Disp`, `#30`		dispense, quantity 30
`RF`		refills
`ud`	ut dictum	as directed
`DAW`		dispense as written, no generic swap

Abbreviations that lead to mistakes

Since 2004, US hospitals accredited by The Joint Commission have had to follow its “Do Not Use” list. The Institute for Safe Medication Practices (ISMP) keeps a longer list of error-prone abbreviations, last revised in 2024. They still turn up on labels and handwritten notes. The decoder flags them in yellow.

Written	Mistaken for	Safer to write	List
`U`, `u`	0, 4 or cc	units	Joint Commission
`IU`	IV or 10	units	Joint Commission
`QD`, `q.d.`	qid, four times a day	daily	Joint Commission
`QOD`	qd or qid	every other day	Joint Commission
`1.0 mg`	10 mg	1 mg	Joint Commission
`.5 mg`	5 mg	0.5 mg	Joint Commission
`MS`, `MSO4`, `MgSO4`	morphine and magnesium sulfate, one for the other	the full drug name	Joint Commission
`µg`	mg, a dose 1,000 times bigger	mcg	ISMP
`cc`	u (units)	mL	ISMP
`SC`, `SQ`	SL (under the tongue), “5 every”	SUBQ or subcut	ISMP
`OD`, `OS`, `AD`, `AS` …	each other; in the UK, OD also means once daily	right eye, left ear and so on	ISMP
`TIW`, `BIW`	three times a day, twice a day	3 times weekly, 2 times weekly	ISMP
`D/C`	discharge or discontinue	the word itself	ISMP
`1/2 tablet`	1 or 2 tablets	half tablet	ISMP
`@`	the number 2	at	ISMP

Everything on the Joint Commission list is on the ISMP list too.

Questions

Is q8h the same as three times a day?

Not quite. q8h means every 8 hours around the clock, for example at 6 am, 2 pm and 10 pm. tid means three times during the day, often with meals, so the gaps can be uneven and the night is free. If you're not sure whether to wake up for a dose, ask the pharmacist.

What does prn mean on a prescription?

It stands for pro re nata, as needed. You take the medicine when you have the symptom, not on a schedule. Labels often add a limit, such as “max 3/day”. Don't go over it.

What's the difference between hs and qhs?

hs means at bedtime, and qhs means every night at bedtime. Both say the same thing for a daily medicine: take it before you go to sleep.

What does Sig mean?

Sig is short for the Latin signa, “label”. The text after it is what the pharmacy prints on your label: the dose, how often and for how long.

Why do prescriptions still use Latin?

Habit and speed. The codes are short and every pharmacist knows them. Many hospitals now ask for plain English instead, and safety groups such as ISMP recommend it.

Is what I type saved anywhere?

No. The decoder runs in your browser. Nothing is sent or stored.

From the label to reminders in one line. Type “1 tab bid” into GottaDose and you get two reminders a day. It knows bid, tid and qid in 7 languages and can read the box with your camera. Coming soon to the App Store.

See what GottaDose does

The decoder spells out abbreviations and doesn't give medical advice. If the result doesn't match what your doctor told you, ask the pharmacist before you take the medicine. Also free: the refill date calculator.