Latin served a good purpose on prescriptions when they were first written in the 1400s. Spread widely by Roman soldiers and traders, Latin was the main language of western Europe for hundreds of years. It was unlikely to change, because it was a "dead" language, and it was unlikely to be misinterpreted, because it was exact in its meaning. Of course, the patients who didn't know Latin probably didn't have the vaguest idea what they were taking.
The only part of a prescription where Latin appears today, however, is in the directions for taking the drug. This use has become a kind of medical shorthand. (See chart.) Some of these abbreviated terms have the potential to cause medication errors because they look so similar in handwriting, so their use is on the decline.
Where does the "Rx" for "prescription" come from? Its origins are given variously as an abbreviation of the Latin word "recipe," meaning "take," or as a representation of the astrological sign of Jupiter. This sign was placed on ancient prescriptions to invoke that deity's blessing on the medicine to help the person get well. More recently, the cross at the end of the "R" has been explained as a substitute period.
Provided by FDA Consumer magazine.