primum non nocere
first, to not harm
Notes
A medical precept. Often falsely attributed to the Hippocratic Oath, though its true source is probably a paraphrase from Hippocrates' Epidemics, where he wrote, "Declare the past, diagnose the present, foretell the future; practice these acts. As to diseases, make a habit of two things: to help, or at least to do no harm."