“First do no harm” – fundamental of medical ethics.

Except dubious origins… The Latin makes people think it’s Hippocrates and in the Hippocratic oath – but Hippocrates was Greek and it’s not in the oath. He does say something pretty similar in the Epidemics.

Not in the Oxford English Dictionary. Well known in America in the 1930s.

1860 Medical Textbook by Inman says it comes from Thomas Sydenham, but not found in his work, and no one else confirms this. But Sydenham did like Latin.

Florence Nightingale says it in English in the preface to her book on hospitals but not in Latin.

Jack Eckert reckons it was the Latin versions of Hippocrates that started to circulate as printed versions that gave rise to the expression. But still odd that rarely used in either English or Latin until second half of 20th century.

Of course, it isn’t a great principle in any case. Most of medicine is a risk:benefit calculation, rather than avoidance of any possible harm.

Lots more discussion in Cedric Smith’s article.