What does Rx stand for in regard to prescriptions?

The R stands for the Latin word recipe, meaning “take,” but there’s more to it than that. Rx is actually taken from the symbol for the planet Jupiter. Look in The Old Farmer’s Almanac under the names and characters of the principal planets and aspects (page 42 in the 2001 Almanac) and you’ll see the symbol for Jupiter, which looks like a fancy number 4, with the diagonal line of the upper left part of the numeral more curved, much like the upper right portion of a capital R. A little stretch of the imagination takes you from that symbol to Rx, where the tail of the R is crossed by the x. Many pharmacies still use the ancient symbol, with the x hanging well below the tail of the R. In the Middle Ages, many physicians and herbalists believed that the planets ruled people’s health, as well as the various plants and shrubs used as remedies. If you read the 16th-century books of the English herbalist Nicholas Culpeper, these planetary influences are apparent in his advice. For some reason, Jupiter—perhaps because it’s so large—was considered the foremost influence in curing diseases, so its symbol came to be used to identify sources of pharmaceuticals, as well as the prescriptions themselves. To the ancients, the planets and their ruling gods were inseparable. Thus, according to Brewer’s Dictionary of Phrase and Fable, the Rx symbol actually says, more or less, “Under the good auspices of Jove, the patron of medicines, take the following drugs in the proportions set down.”