How to read prescription abbreviations: a complete decoder (OD, BD, TDS, PRN, a.c., 1+0+1)

Almost every prescription in Bangladesh — and around the world — is written in a shorthand of Latin and medical codes: OD, BD, TDS, 1+0+1, a.c., PRN, and dozens more. Learning how to read prescription abbreviations is one of the most useful pieces of health literacy you can have. It tells you how many times a day to take a medicine, whether to take it before or after food, at night or in the morning, and whether a dose is fixed or only "as needed". This guide is a complete, accurate decoder of the prescription abbreviations you are most likely to see, written for patients and for junior doctors and pharmacy staff who want a reliable reference.

Before we start, one rule matters more than every code below: this guide explains what the abbreviations usually mean, but it does not replace the instruction your own doctor or pharmacist gives you. Handwriting varies, local conventions differ, and a single misread letter can change a dose. If anything on your prescription is unclear — or if our decoding does not match what you were told — always confirm with the doctor who wrote it or the pharmacist who dispenses it before you take a single dose. Use this page to understand and to ask better questions, not to self-medicate.

How a prescription is structured

It helps to know the anatomy of the page before decoding the codes. A typical prescription has four parts, a structure that has barely changed since Latin was the language of medicine:

• The superscription — the patient's details and the Rx symbol at the top. "Rx" is an abbreviation of the Latin recipe, meaning "take" or "take thou"; it is the instruction that opens the order.
• The inscription — the medicines themselves: the drug name, its strength (for example 500 mg), and the form (tablet, capsule, syrup).
• The subscription — instructions to the pharmacist, such as how much to dispense.
• The signatura, or "Sig" — the directions for you, the patient: how much to take, how often, by which route, and when. This is where the famous abbreviations like BD, TDS and PRN live. The codes in the Sig line are often called sig codes or Rx abbreviations.

Most of the confusion patients feel comes from the Sig line, so that is where this decoder spends most of its time. If you also want to understand the rules a doctor follows when writing this page, our guide to prescription writing rules in Bangladesh walks through the legal and clinical requirements in detail.

The complete prescription abbreviations decoder

Here is the master reference. The first table covers the frequency and timing codes — how often and when to take a medicine — because these are the ones patients most need to read correctly. Every meaning shown is the standard, internationally recognised definition; where an abbreviation is considered risky, the table says so.

Abbreviation	From (Latin)	Meaning
OD	omni die / once daily	Once a day. (Internationally, OD is discouraged because it can also be misread as "right eye" — see the safety note below.)
OM / mane	omni mane	In the morning.
ON / nocte	omni nocte	At night.
BD / BID	bis in die	Twice a day (usually morning and night).
TDS / TID	ter die sumendus / ter in die	Three times a day.
QID / QDS	quater in die / quater die sumendus	Four times a day.
QD	quaque die	Every day / once daily. (Discouraged — easily confused with QID; "daily" should be written in full.)
QOD / alt. die	quaque altera die	Every other day (alternate days).
HS	hora somni	At bedtime ("hour of sleep").
q4h, q6h, q8h, q12h	quaque … hora	Every 4 / 6 / 8 / 12 hours.
PRN	pro re nata	As needed (only when the symptom is present — e.g. for pain or fever).
SOS	si opus sit	If necessary — usually one dose, taken only if required.
STAT	statim	Immediately, at once (a single, right-now dose).
a.c.	ante cibum	Before food / before meals.
p.c.	post cibum	After food / after meals.
c.c. / pc	cum cibo	With food.
1+0+1	Bangladeshi notation	Morning + noon + night: take 1 dose in the morning, 0 at noon, 1 at night (also written 1-0-1).

The second table decodes the route (how the medicine enters the body), the dosage form, and the quantity/measurement abbreviations. These appear in the inscription and Sig lines and matter just as much — giving an oral medicine by the wrong route, for example, is a serious error.

Abbreviation	From (Latin)	Meaning
PO	per os	By mouth (orally).
SL	sub lingua	Under the tongue (sublingual).
IV	intravenous	Into a vein (by injection/drip).
IM	intramuscular	Into a muscle (by injection).
SC / S/C	subcutaneous	Under the skin (by injection).
PR	per rectum	Into the rectum (e.g. a suppository).
PV	per vaginam	Into the vagina.
top.	topical	Applied to the skin surface.
inh.	inhalation	Breathed in (e.g. an inhaler or nebuliser).
tab	tabella	Tablet.
cap	capsula	Capsule.
syp / syr	syrupus	Syrup.
susp	suspension	Suspension (a liquid to shake before use).
inj	injectio	Injection.
oint / ung.	unguentum	Ointment.
gtt	guttae	Drops (e.g. eye or ear drops).
aa	ana	Of each (equal amounts).
q.s.	quantum sufficit	A sufficient quantity (as much as needed).
tsp / tbsp	teaspoon / tablespoon	≈ 5 mL / ≈ 15 mL (use the measuring cap, not a kitchen spoon).
mg / mcg / g / mL	units of measure	Milligram / microgram / gram / millilitre (strength or volume).

You do not need to memorise every line. Most everyday prescriptions in Bangladesh use a small core: a form (tab/cap/syp), a strength (e.g. 500 mg), a frequency (OD/BD/TDS or 1+0+1), a relation to food (a.c./p.c.), and a duration ("× 7 days"). Once you can read those five, you can read the majority of prescriptions you will ever hold.

Understanding frequency: OD, BD, TDS, QID and HS

The frequency code tells you how many times in 24 hours to take a dose, and getting it right is the single most important reading skill. The pattern is built from Latin number words: bis (two) gives BD = twice daily, ter (three) gives TDS = three times daily, and quater (four) gives QID/QDS = four times daily. A medicine marked OD is taken once a day, and one marked HS is taken at bedtime — common for medicines that cause drowsiness, like some antihistamines, or for night-time stomach protection.

A frequency on its own does not fix the exact clock time — your pharmacist or the medicine label will usually suggest sensible spacing. A "three times a day" antibiotic, for instance, is best spread roughly every eight hours rather than crammed into the daytime, so the drug level in your blood stays steady. If your prescription pairs a frequency with a food instruction (say "TDS p.c."), that means three times a day, each dose after a meal.

What the Bangladeshi 1+0+1 notation means

Many Bangladeshi doctors write dosing as a three-number pattern such as 1+0+1 (sometimes 1-0-1). Read it left to right as morning + noon + night. So:

• 1+0+1 = one dose in the morning, none at noon, one at night (twice a day).
• 1+1+1 = one dose morning, noon and night (three times a day).
• 0+0+1 = one dose at night only.
• ½+0+½ = half a tablet morning and night.

The number is the quantity of tablets (or spoonfuls of syrup) for that time of day, and a 0 simply means "skip that slot". It is a clear, patient-friendly system precisely because it shows the time of day and the amount together. If your doctor has also written a food instruction, apply it to each non-zero dose.

As-needed and urgent doses: PRN, SOS and STAT

Three codes change a medicine from "take on a schedule" to "take only in a particular situation", and confusing them is a common cause of over- or under-dosing.

• PRN (pro re nata) means as needed. A painkiller written "1 tab PRN for pain" is taken only when you have pain — not on a fixed timetable. A good PRN instruction also states a minimum gap and a daily maximum (for example "up to every 6 hours, maximum 4 a day"); if yours does not, ask the pharmacist what the safe limit is.
• SOS (si opus sit) means if necessary, and in everyday Bangladeshi practice usually implies a single dose taken only if the problem occurs — for example one tablet for a one-off bout of nausea.
• STAT (statim) means immediately — a single dose to be taken right now, often the first dose of a course or an urgent medicine.

The key safety point with PRN and SOS medicines is the ceiling. Because there is no fixed schedule, it is easy to take too many in a day. Always know the maximum number of doses in 24 hours before you start, and never treat "as needed" as "as often as I like".

Timing around food: a.c., p.c. and with food

Whether a medicine is taken before or after food is not a minor detail — for some drugs it changes how well they are absorbed or how kindly they sit in the stomach. The two codes you will see most are a.c. (ante cibum, before food) and p.c. (post cibum, after food). "Before food" usually means on a fairly empty stomach, often about 30 minutes before a meal; "after food" means with or just after eating, which cushions medicines that can irritate the stomach. If a drug is marked simply "with food", take it during the meal.

These instructions exist for a reason. Some medicines work best on an empty stomach; others — many painkillers and certain antibiotics among them — are written p.c. specifically to protect your stomach lining. If your prescription does not say and you are unsure, that is exactly the kind of question a pharmacist answers in seconds.

A serious word on look-alike abbreviations

Not all abbreviations are equally safe, and this is where reading them yourself has limits. Several shorthand forms have been linked to real dosing errors worldwide and now appear on official "do not use" lists in many health systems:

• OD can mean "once daily" but is also the abbreviation for oculus dexter, the right eye — a tablet meant to be swallowed once a day could be misread as an eye instruction.
• QD (once daily) and QID (four times daily) look almost identical in hurried handwriting, yet differ four-fold in dose.
• U for "units" can be misread as a zero or a four, turning 4U into 40 or 44 — which is why insulin and similar doses should spell out "units".
• A trailing zero (writing "1.0 mg") can be misread as 10 mg, and a missing leading zero (".5 mg" instead of "0.5 mg") can be misread as 5 mg.

The lesson is not to distrust your prescription, but to respect the ambiguity: if a dose looks surprising, a number is hard to read, or a unit is unclear, do not guess — confirm. This is also why printed prescriptions are safer than handwriting. If you are a doctor, you can sidestep all of these traps by writing clean, typed prescriptions in our free prescription generator, which keeps drug names, strengths and frequencies legible on every page.

Safety first: never self-medicate from decoding alone

This is the most important section on the page. Being able to read an abbreviation is not the same as being qualified to act on it. Decoding tells you what a code means in general; it cannot tell you whether a medicine is right for your condition, your other medicines, your kidneys and liver, your pregnancy, or your allergies — those are clinical judgments only your prescriber can make. Use this guide to understand your own prescription and to ask sharper questions, never to start, stop, change or share a medicine on your own.

If anything is unclear — an abbreviation you cannot place, a dose that seems too high or too low, a frequency that does not match what you were told, or two medicines you are unsure about taking together — stop and confirm with the doctor who wrote the prescription or the pharmacist who dispenses it. Pharmacists in particular are an under-used safety net: checking an unclear instruction with them takes a minute and prevents real harm. When you want to know more about the medicine itself — its uses, strengths and generic name — you can also look it up in our medicine directory, but treat that as background reading, not a substitute for professional advice.

For doctors: write prescriptions people can actually read

If you are the one writing the page, the safest abbreviation is the one that cannot be misread. Best practice — and the direction every modern guideline points — is to keep frequency codes standard (BD, TDS, OD), avoid the risky forms (QD, U, trailing zeros), and, wherever the layout allows, support the code with plain wording the patient understands. A printed prescription does most of this for you by making every line legible. Our guides on how to make a prescription online for free and on choosing free e-prescription software in Bangladesh walk through the practicalities, and who can write a prescription in Bangladesh covers who is authorised to issue one in the first place.

ChamberBD's free prescription generator lets you write a clean, branded, printable prescription in the browser — no sign-up — with drug names drawn from a database so spellings and strengths stay correct. When you want the prescription to remember the patient, with history, permanent links and SMS reminders, you can create a free ChamberBD account and keep the whole chamber in one place.

Putting it together: reading a real line

Imagine your prescription reads: Cap. Amoxicillin 500 mg — 1 cap TDS p.c. × 7 days. Decoded, that is: an Amoxicillin capsule of 500 mg strength, take one capsule, three times a day (TDS), after food (p.c.), for seven days. Or in Bangladeshi notation: Tab. Paracetamol 500 mg — 1+1+1 PRN for fever means a 500 mg paracetamol tablet, one in the morning, noon and night, but only as needed for fever. Once the codes click into place, the whole page becomes plain language.

That is the goal of this guide: not to turn you into your own doctor, but to let you hold your prescription and understand it — so you take your medicine correctly, and so you know exactly which questions to ask when something is not clear.

Frequently Asked Questions

What does 1+0+1 mean on a prescription?

1+0+1 (also written 1-0-1) is the Bangladeshi morning-noon-night dosing notation. Read left to right, it means take 1 dose in the morning, 0 (none) at noon, and 1 dose at night — so twice a day. The numbers are the quantity for each time of day, and a 0 means skip that slot. For example, 1+1+1 is three times a day, and 0+0+1 is once at night only. If a food instruction is also written, apply it to each non-zero dose.

What does BD and TDS mean on a prescription?

BD (from the Latin bis in die) means twice a day, usually morning and night. TDS (from ter die sumendus, also written TID) means three times a day, ideally spaced roughly every eight hours. Related codes are OD (once daily), QID or QDS (four times daily) and HS (at bedtime). The frequency tells you how many doses to take in 24 hours; your pharmacist or the medicine label can suggest the best spacing.

What is the difference between PRN and SOS?

PRN (pro re nata) means "as needed" — you take the medicine only when the symptom is present, such as a painkiller for pain, often with a stated minimum gap and daily maximum. SOS (si opus sit) means "if necessary" and in everyday practice usually implies a single dose taken only if the problem occurs. With both, always know the maximum number of doses allowed in 24 hours before you start, and never treat "as needed" as "as often as I like".

What does a.c. and p.c. mean on a prescription?

a.c. stands for the Latin ante cibum and means before food (usually on a fairly empty stomach, often about 30 minutes before a meal). p.c. stands for post cibum and means after food (with or just after eating). These instructions matter: some medicines are absorbed better on an empty stomach, while many painkillers and antibiotics are taken after food to protect the stomach. If your prescription does not specify and you are unsure, ask the pharmacist.

Is it safe to take medicine based on the abbreviation alone?

No. Knowing what an abbreviation means is not the same as knowing whether a medicine is right for you. Decoding cannot account for your other medicines, allergies, kidney or liver function, pregnancy, or your specific condition — only your prescriber can. Handwriting can also be misread, and some abbreviations (like OD, QD and U) are known to cause errors. Always confirm anything unclear with the doctor who wrote the prescription or the pharmacist who dispenses it before taking a single dose, and never start, stop or change a medicine on your own.

Decoding the codes on your prescription is genuinely useful health literacy — but it is the beginning of a conversation, not the end of one. Read your prescription, look the medicine up in our medicine directory for background, and confirm anything unclear with your doctor or pharmacist. If you are a doctor who wants every line to be legible from the start, write your next prescription free in the prescription generator or create a free ChamberBD account to keep records, reprints and reminders in one place.