Medical abbreviations on a prescription
Prescriptions compress the instructions into Latin shorthand called sig codes. PO is by mouth, BID is twice a day, TID three times a day and PRN means only as needed. Look up any abbreviation below, or read the worked examples to decode a full line.
Quick lookup
| Abbreviation | Means | From |
|---|---|---|
| AC | before meals | ante cibum |
| BID | twice a day | bis in die |
| cap | capsule | capsula |
| Disp | dispense (quantity to supply) | dispensa |
| gtt | drops | guttae |
| IM | intramuscular | — |
| IV | intravenous | — |
| NPO | nothing by mouth | nil per os |
| ODerror-prone | right eye — or once daily, depending on country | oculus dexter / omni die |
| PC | after meals | post cibum |
| PO | by mouth | per os |
| PR | by the rectum | per rectum |
| PRN | as needed | pro re nata |
| Q12H | every 12 hours | quaque 12 hora |
| Q4H | every 4 hours | quaque 4 hora |
| Q6H | every 6 hours | quaque 6 hora |
| Q8H | every 8 hours | quaque 8 hora |
| QAM | every morning | quaque ante meridiem |
| QDerror-prone | once a day | quaque die |
| QHSerror-prone | every night at bedtime | quaque hora somni |
| QID | four times a day | quater in die |
| QODerror-prone | every other day | quaque altera die |
| QPM | every evening | quaque post meridiem |
| Rx | prescription / take | recipe |
| SIG | write / label the instructions | signa |
| SL | under the tongue | sub lingua |
| SQerror-prone | subcutaneous | — |
| STAT | immediately | statim |
| tab | tablet | tabella |
| TID | three times a day | ter in die |
Reading a full sig line
Abbreviations stack in a fixed order: how much, what form, which route, how often, then any condition. Read them left to right.
1 tab PO QD
Take one tablet by mouth once a day.
1 tab PO BID
Take one tablet by mouth twice a day, morning and evening.
PO TID PRN pain
By mouth, up to three times a day, only when you have pain — none if you have no symptoms.
1 cap PO QID AC
Take one capsule by mouth four times a day, each dose before a meal.
2 tabs PO Q6H PRN, max 8 tabs/24h
Take two tablets by mouth no more often than every six hours as needed, and no more than eight tablets in 24 hours.
10 mg PO QHS
Take 10 mg by mouth every night at bedtime.
Disp: 21 caps. Sig: 1 cap PO TID x 7 days
Supply 21 capsules; take one by mouth three times a day for seven days.
Abbreviations flagged as error-prone
These appear on the ISMP List of Error-Prone Abbreviations because they are routinely misread as one another. If you see one on a handwritten prescription and the pharmacy label does not spell the instruction out, confirm it before the first dose.
Grouped by what they tell you
How to take it
How often
When
What form
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This reference explains prescription notation for general information. It is not medical advice and does not replace your prescriber or pharmacist. If a label is unclear or differs from what you were told, check with your pharmacy before taking the medicine.