Prescription abbreviations
What SOS means
on a prescription.
SOS on a prescription means take the medicine only when it’s needed, not on a fixed schedule. It comes from the Latin si opus sit, “if there is a need”, and is used on prescriptions in India and Pakistan. American and British prescriptions write the same idea as PRN.
SOS
only when needed
si opus sit, Latin for “if there is a need”
Also written s.o.s.
What counts as needed
The prescription or the doctor should say what the medicine is for, such as pain or fever, and how often it may be taken. If it doesn’t, ask the pharmacist before taking it.
SOS doesn’t mean once
A few websites say SOS means a single dose. The references we checked define it as when needed.
Setting it up in AlongWell
Choose When needed as the schedule. AlongWell sends no reminders for it; you log a dose each time it’s taken, as often as that is.
Questions
What does SOS mean on a prescription?
Take the medicine only when it’s needed. SOS comes from the Latin si opus sit, “if there is a need”.
Is SOS the same as PRN?
Yes. Both mean as needed. SOS is used in India, PRN in the US and UK.
How often can I take an SOS medicine?
The prescription or the label should say. If it doesn’t, ask your doctor or pharmacist before taking it.
Sources
- Shetty Y and others, Indian Journal of Medical Research, 2024, read 28 October 2026
- Patel MJ and others, PLoS ONE, 2013, read 28 October 2026
- Partial list of prescription abbreviations (mn.gov), read 28 October 2026
This page explains what an abbreviation means. It doesn’t say how much to take or when: follow what the doctor wrote, and ask your pharmacist if any part of a prescription is unclear.
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