Prescription abbreviations
What PRN means
on a prescription.
PRN on a prescription means as needed: take the medicine only when you need it, not on a fixed schedule. It comes from the Latin pro re nata and is used on American and British prescriptions, where it may be written “when required”. On Indian prescriptions the same idea is written SOS.
PRN
as needed
pro re nata, Latin for “as needed”
Also written p.r.n.
PRN and SOS
They mean the same. PRN is used in the US and UK, SOS in India.
What the prescription should add
UK prescribing standards ask for an as-needed prescription to state the shortest time between doses and the most that may be taken. If yours doesn’t, ask the pharmacist.
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 PRN mean on a prescription?
As needed. PRN comes from the Latin pro re nata.
Is PRN the same as SOS?
Yes. Both mean as needed. PRN is used in the US and UK, SOS in India.
Sources
- ISMP Consumer Medication Safety: Learn to read a prescription, read 28 October 2026
- MedlinePlus: Some common abbreviations, read 28 October 2026
- College of Optometrists (UK): pharmacy and drug terms, read 28 October 2026
- Wye Valley NHS Trust: Prescription writing standards, read 28 October 2026
- Shetty Y and others, Indian Journal of Medical Research, 2024, 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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