Rx is commonly considered an abbreviation for the Latin word recipere or recipe, which means “Take, thou.” Additional medical abbreviations also use x: For example, sx = signs and symptoms, tx = treatment, hx = history, and dx = diagnosis.
However, the Rx symbol is not really the standard letters “R” and “x,” but actually a symbol of an italic R with a leg that hangs down below the line with a line crossing it like an x, which is thought to refer to the Roman god Jupiter (which looks like a fancy number 4) – to invoke his blessing on the drug to help the patient recover.
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. According to the 16th-century English herbalist Nicholas Culpeper, Jupiter–perhaps because it’s so large–was considered the foremost influence in curing diseases. Thus its symbol came to be used to identify sources of pharmaceuticals, as well as the prescriptions themselves. The ancients associated the planets directly with their ruling gods. According to Brewer’s Dictionary of Phrase and Fable, the Rx symbol can be loosely translated as, “Under the good auspices of Jove, the patron of medicines, take the following drugs in the proportions set down.”
There are two theories offered to explain why Roman physicians would have written Jupiter’s symbol on their prescriptions. The first is that physicians would typically offer a prayer to Jupiter asking for protection over their patient. To shorten this process, doctors began writing the symbol for the planet Jupiter on prescriptions.
The second explanation is that during Emperor Nero’s oppression of Christianity in the first century, physicians would write Jupiter’s symbol on medical documents, including prescriptions, to demonstrate their rejection of Christianity and their support of Roman religion.
However, there’s yet another theory behind the Rx symbol origins. Within Egyptian mythology, the Sun god Horus lost his eye to an attack from Seth, an evil deity. However, Horus’ mother invoked Thoth, the god of learning and magic, who healed the eye of Horus. As such, the eye of Horus served as a symbol of healing and protection in ancient Egypt. Physicians would use amulets of the eye in their medical rituals, and both the living and the dead would wear these amulets for protection.
Long after the fall of the ancient Egyptian civilization, doctors and alchemists in Europe continued the custom of showing a sign of divine help and protection. But over the years, the sign morphed from the eye of Horus to the sign for Jupiter, and eventually to the modern “Rx” symbol. “Rx” no longer symbolizes heavenly protection for the sick, but signifies “take this medicine.”