What does bid mean on a prescription?

'bid' means twice a day (from the Latin bis in die). tid is three times a day and qid is four times a day. Your pharmacy label should also spell out the plain-English directions — follow those, and ask your pharmacist if anything is unclear.

'prn' means 'as needed' (pro re nata) — you take the medicine only when you need it (for example, for pain), up to any maximum the label states. 'po' means by mouth.

What does qid vs qd mean?

'qid' is four times a day; 'qd' is meant to be once a day — but 'qd' is easily misread as 'qid', so safety groups (ISMP) discourage it and ask prescribers to write 'daily'. If you see it, confirm with your pharmacist.

Should I rely on these abbreviations to take my medicine?

No. Use them to understand your prescription, but always follow the plain-language directions on your pharmacy label and confirm with your pharmacist. Several abbreviations are ambiguous and can be misread — that's why many are being phased out.

Prescription abbreviations, decoded

The short Latin codes on a prescription — bid, tid, qid, prn, poand the rest — in plain English. We’ve also flagged the ones drug-safety experts consider error-prone, because a few are easy to misread.

By the pharmaranks editorial teamReviewed against ISMP & MedlinePlus (NLM) sourcesHow we research

Use this to understand — not to self-dose

This is a general reference. Some abbreviations are ambiguous and can be misread, so always follow the plain-language directions on your pharmacy label and confirm anything unclear with your pharmacist. Items marked ⚠️ error-prone are ones the Institute for Safe Medication Practices recommends prescribers stop using.

How often (frequency & timing)

bid	Twice a day · bis in die
tid	Three times a day · ter in die
qid	Four times a day · quater in die
qd / q.d.⚠️	Once a day · quaque dieThe ISMP discourages 'qd' — it's easily misread as 'qid'. Prescribers should write 'daily'.
qod⚠️	Every other dayISMP discourages — mistaken for 'qd' or 'qid'. Should be written 'every other day'.
q4h / q6h / q8h / q12h	Every 4 / 6 / 8 / 12 hours · quaque
prn	As needed · pro re nata
hs / qhs⚠️	At bedtime · hora somni'hs' can be misread as 'half-strength'.
ac	Before meals · ante cibum
pc	After meals · post cibum
stat	Immediately · statim

How to take it (route)

po	By mouth · per os
sl	Under the tongue (sublingual)
pr	Rectally · per rectum
top	On the skin (topically)
inh	Inhaled
SC / SubQ⚠️	Under the skin (subcutaneous)ISMP: spell out 'subcut' or 'subcutaneously' — 'SC' can be read as 'SL'.
IM	Into a muscle (intramuscular)
IV	Into a vein (intravenous)
OD / OS / OU⚠️	Right eye / left eye / both eyesISMP discourages — 'OD' is also mistaken for 'once daily'. Should be spelled out.
AD / AS / AU⚠️	Right ear / left ear / both earsAlso discouraged for the same reason as the eye codes.

How much & what form

tab / cap	Tablet / capsule
gtt	Drop(s) · gutta
mL	Milliliters
mg / mcg / g	Milligrams / micrograms / grams'mcg' is preferred over the older 'µg', which can be misread as 'mg'.
ung	Ointment · unguentum
supp	Suppository
ss⚠️	One-half · semisISMP: mistaken for '55' — should be written 'one-half' or '½'.

On the label & other

Rx	Prescription / 'take' · recipe
Sig	The directions for the patient · signa (let it be labeled)
disp	Dispense (the amount to give you)
qs	A sufficient quantity · quantum satis
NPO	Nothing by mouth · nil per os
U / IU⚠️	Units / international unitsISMP: 'U' is mistaken for '0' or '4', and 'IU' for 'IV' — both should be spelled out ('units').

FAQ

What does bid mean on a prescription?: 'bid' means twice a day (from the Latin bis in die). tid is three times a day and qid is four times a day. Your pharmacy label should also spell out the plain-English directions — follow those, and ask your pharmacist if anything is unclear.
What does prn mean?: 'prn' means 'as needed' (pro re nata) — you take the medicine only when you need it (for example, for pain), up to any maximum the label states. 'po' means by mouth.
What does qid vs qd mean?: 'qid' is four times a day; 'qd' is meant to be once a day — but 'qd' is easily misread as 'qid', so safety groups (ISMP) discourage it and ask prescribers to write 'daily'. If you see it, confirm with your pharmacist.
Should I rely on these abbreviations to take my medicine?: No. Use them to understand your prescription, but always follow the plain-language directions on your pharmacy label and confirm with your pharmacist. Several abbreviations are ambiguous and can be misread — that's why many are being phased out.

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Sources

General reference, not medical advice. Prescription abbreviations can be ambiguous — always follow your pharmacy label’s plain-language directions and confirm with your pharmacist or prescriber before taking any medicine.