BID means twice a day, TID means three times a day, QID means four times a day and PRN means as needed. Rx simply means prescription. If anything on a prescription or label is unclear, ask your pharmacist before you take it.
These short forms come from medical shorthand. Your pharmacy label should normally spell out the directions in plain words, so go by the label and check anything that does not match what your doctor told you.
The common ones
| Abbreviation | Meaning |
|---|---|
| Rx | Prescription |
| BID | Twice a day |
| TID | Three times a day |
| QID | Four times a day |
| PRN | As needed |
These meanings come from MedlinePlus's list of common abbreviations. For more on as-needed doses, read what PRN means.
What "twice a day" does not tell you
An abbreviation gives you how often, and often not when. Twice a day could mean morning and night, or something more specific. Ask your pharmacist:
- What times should I take this?
- Does it matter whether I take it with food?
- Should it be kept apart from any of my other medicines?
- What should I do if I miss a dose?
Why it's fine to ask
Abbreviations can cause real mistakes. The Institute for Safe Medication Practices keeps a list of abbreviations, symbols and dose designations that have been misread and involved in harmful or potentially harmful medication errors, and says they should never be used. Your pharmacist would much rather answer a question than have you guess.
If a label is hard to read
- Ask for a clearer label. Your pharmacy may be able to help with larger print.
- Have the directions explained when you collect it, especially if it is a new medicine. See starting a new prescription.
- Keep the leaflet. It has the details a label can't fit.
- Do not rely on memory. Write the directions into your medication list.
Your phone can help with typing it in. Cadence can scan a prescription label to fill in the details, and you should check them against the label afterwards.
Frequently asked questions
What does BID mean on a prescription?
Twice a day. Ask your pharmacist what times suit your medicine.
What is the difference between TID and QID?
TID means three times a day and QID means four times a day.
What does PRN mean?
As needed. Your label or doctor should tell you what it is for and any limit that applies.
What does Rx stand for?
MedlinePlus lists it as short for prescription.
Sources
Some common abbreviations, MedlinePlus. List of error-prone abbreviations, Institute for Safe Medication Practices.
Cadence is a free medication reminder app for iPhone and Apple Watch. It is not medical software and does not give medical advice. Cadence Pro is a one-time purchase, with no subscription.
