The Origins of Using "Rx" for "Prescription"
The origin of "Rx", used as an abbreviation for "prescription", has been attributed to the Latin word "recipe" which means "take". Also, it has been associated with Jupiter, the chief deity of Roman state religion until Christianity became the dominant religion of the Roman Empire. The symbol was placed on prescriptions to invoke the deity's blessing on the medicine to help a person get well. More recently, the cross that sometimes appears at the end of the "R" has been explained as a substitute period.
The Use of Prescription Abbreviations: An Example
An example of what your doctor may write:
Sig: I tab po qid pc & hs
Unless you have a medical background, our example may be unintelligible. In this example, the prescription abbreviations instruct the pharmacist to, "Label the container for this patient's medication with the following instructions: Take one tablet by mouth 4 times a day, after meals and at bedtime."
Common Latin Rx Terms
Some of the common latin prescription abbreviations include:
- ac (ante cibum) means "before meals"
- bid (bis in die) means "twice a day"
- gt (gutta) means "drop"
- hs (hora somni) means "at bedtime"
- od (oculus dexter) means "right eye"
- os (oculus sinister) means "left eye"
- po (per os) means "by mouth"
- pc (post cibum) means "after meals"
- prn (pro re nata) means "as needed"
- q 3 h (quaque 3 hora) means "every 3 hours"
- qd (quaque die) means "every day"
- qid (quater in die) means "4 times a day"
- Sig (signa) means "write"
- tid (ter in die) means "3 times a day"
For an In-Depth Listing of Prescription Abbreviations:
Use of Abbreviations Is Slowly in Decline
While the Latin terms are still commonly seen on prescriptions, some doctors are gradually retiring use of these old terms and better clarifying their drug orders in plain language.
Since improved readability helps prevent medication mix-ups, it has been recommended that prescribers write out instructions rather than use more ambiguous abbreviations. For example, prescribers would write "daily" rather than "qd", the abbreviated Latin term for "every day". In this case, "qd" could easily be misinterpreted as "qid" (which means 4 times a day) or "od" (which means right eye).
The Bottom Line
If the directions written on a prescription are unclear or confusing, please ask your doctor or pharmacist to explain. Do not take your medication without fully understanding the prescribing instructions.
Master List of Prescription Abbreviations. Accessed 08/22/13.
Making It Easier to Read Prescriptions, by Dixie Farley, FDA Consumer Magazine, July-August 1995