What does SOS mean on a prescription?

SOS usually means the medicine should be taken only if needed, not on a fixed schedule. Ask your pharmacist about the maximum safe dose in 24 hours.

Prescription safety guide

Prescription Abbreviations Dictionary

Q: What does BD mean on a prescription?

BD usually means twice daily. Always confirm timing and dosage with a pharmacist or doctor if the prescription is unclear.

Q: What does OD mean on a prescription?

OD is often used to mean once daily, but it can also be confused with eye-related abbreviations in some contexts. Always verify unclear prescriptions with a pharmacist.

Confused by terms like BD, OD, SOS, TDS, AC or PC on a prescription? This simple dictionary explains common doctor shorthand in plain English, so you can better understand your prescription before confirming it with a pharmacist or doctor.

Important: This page is for educational purposes only. Never guess a dose, timing, medicine name, or abbreviation. If anything is unclear, confirm it with a licensed pharmacist or doctor.

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Common Prescription Abbreviations and Meanings

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Abbreviation	Common meaning	Plain English explanation	Safety note
BD / BID	Twice daily	Usually means the medicine should be taken two times in one day.	Ask whether doses should be morning/evening or 12 hours apart.
TDS / TID	Three times daily	Usually means the medicine should be taken three times in one day.	Confirm if it should be taken with meals or at fixed intervals.
OD / QD	Once daily	Usually means the medicine should be taken one time per day.	OD can be confused in some contexts. Verify unclear handwriting.
QID	Four times daily	Usually means four doses in one day.	Do not confuse with QD/OD. Ask for exact timing.
SOS	If needed	The medicine is usually taken only when symptoms appear.	Ask the maximum safe dose in 24 hours.
PRN	As needed	Similar to SOS; not usually a fixed schedule.	Clarify when to use it and when to stop.
AC	Before meals	The medicine may need to be taken before eating.	Ask how many minutes before food.
PC	After meals	The medicine may need to be taken after eating.	Useful for medicines that may irritate the stomach.
PO	By mouth	The medicine is usually swallowed orally.	Confirm if it should be swallowed, dissolved, or chewed.
HS	At bedtime	Usually means the medicine is taken before sleep.	Some medicines cause drowsiness. Ask if driving should be avoided.
STAT	Immediately	The dose may be needed right away.	Confirm urgency with the medical professional.
Q4H / Q6H / Q8H	Every 4/6/8 hours	The medicine may need to be taken at repeated hourly intervals.	Ask if this includes night-time doses.
Tab	Tablet	A solid medicine form, usually swallowed.	Do not split unless the pharmacist confirms it is safe.
Cap	Capsule	A capsule form of medicine.	Do not open unless instructed.
Syr	Syrup	Liquid medicine, often measured in mL.	Use a measuring cup or oral syringe, not a kitchen spoon.
Inj	Injection	Medicine given by injection.	Route matters: IM, IV, SC and other routes are not interchangeable.
IV	Intravenous	Medicine given into a vein.	Should only be handled by trained healthcare professionals.
IM	Intramuscular	Medicine injected into a muscle.	Confirm route and dose before use.
SC / SQ	Subcutaneous	Medicine injected under the skin.	Do not confuse with other injection routes.
SL	Sublingual	Medicine placed under the tongue.	Usually should not be swallowed immediately.
GTT	Drops	Often used for eye or ear drops.	Confirm eye vs ear use carefully.
OU / OS / OD	Both eyes / left eye / right eye	These may appear in eye prescriptions.	OD can also be confused with once daily. Always verify context.
Top	Topical	Applied to the skin.	Do not use on eyes, mouth, or broken skin unless instructed.
Neb	Nebulization	Medicine inhaled using a nebulizer.	Confirm dilution and frequency.
Rx	Prescription	Common symbol for a medical prescription.	Does not explain the medicine itself.

Dangerous Abbreviations to Double-Check

U / IU

May be confused with numbers or other letters. Ask the pharmacist to confirm the exact unit.

mg vs mcg

Milligrams and micrograms are very different. This must be read correctly.

QD vs QID

One means once daily; the other can mean four times daily. Messy handwriting can make them look similar.

5.0 mg vs 5 mg

A trailing zero can cause serious confusion if the decimal point is missed.

How to Use This Dictionary Safely

Search the abbreviation you see on the prescription.
Read the plain-English meaning and safety note.
Compare it with the original prescription image.
If anything is unclear, ask a pharmacist before taking or giving the medicine.

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FAQ

What does BD mean on a prescription?

BD usually means twice daily. Ask your pharmacist whether the doses should be taken morning and evening or at fixed intervals.

What does OD mean on a prescription?

OD is often used to mean once daily, but it can also have another meaning in eye prescriptions. Always verify the context.

What does SOS mean?

SOS usually means the medicine is taken only if needed. Ask the pharmacist about the maximum dose allowed in 24 hours.

Can I rely only on this dictionary?

No. This dictionary is educational. A pharmacist or doctor should confirm unclear instructions.