From the website of the Wellcome Collection:
“…Slithering their way through the iconography of pharmaceutical history, snakes appear, often wrapped around a staff, wherever you find apothecaries. Asclepius, the Greek god of medicine, carried a rod with a single snake, which became a medical symbol from the fifth century BCE.
The messenger of the gods, Hermes (the Roman god Mercury), acquired an extra snake on his staff, known as a caduceus. It’s perhaps not a coincidence, then, that the element mercury was a major chemical agent in the history of medicine and alchemy. For example, the evaporated vapour of mercury combined with snake venom was injected through the centre of the scalp as an antidote to snake bite and epilepsy. Both Hermes, the god of commerce, and Mercury, the god of trade, are a good fit for retail pharmacy.
The symmetrical proportions of the caduceus lend themselves to design. It was first used as a printer’s mark (colophon) by a 15th-century book publisher, and its association with medicine was revived in the early 19th century when a medical publisher adopted it. In France, snakes might also be found entwined around palm trees on 19th-century pharmaceutical labels. Perhaps this is a reminder of the exotic origins of many drugs?…”
From the Online Etymology Dictionary:
“late 14c., farmacie, “a medicine that rids the body of an excess of humors (except blood);” also “treatment with medicine; theory of treatment with medicine,” from Old French farmacie “a purgative” (13c.) and directly from Medieval Latin pharmacia, from Greek pharmakeia “a healing or harmful medicine, a healing or poisonous herb; a drug, poisonous potion; magic (potion), dye, raw material for physical or chemical processing.”
This is from pharmakeus (fem. pharmakis) “a preparer of drugs, a poisoner, a sorcerer” from pharmakon “a drug, a poison, philter, charm, spell, enchantment.” Beekes writes that the original meaning cannot be clearly established, and “The word is clearly Pre-Greek.” The ph- was restored 16c. in French, 17c. in English (see ph).
Buck [“Selected Indo-European Synonyms”] notes that “Words for ‘poison’, apart from an inherited group, are in some cases the same as those for ‘drug’ ….” In addition to the Greek word he has Latin venenum “poison,” earlier “drug, medical potion” (source of Spanish veneno, French venin, English venom), and Old English lybb.
Meaning “the use or administration of drugs” is from c. 1400; the sense of “art or practice of preparing, preserving, and compounding medicines and dispensing them according to prescriptions” is from 1650s; that of “place where drugs are prepared and dispensed” is recorded by 1833.”