- "I swear this oath by Apollo Physician by Aesculapius, by Health, and by all the gods and goddesses in whatsoever place that I enter, I will enter to help the sick and heal the injured. And I will do no harm."
A physician, also known as a medical doctor, was a type of medical practitioner, typically holding the title of doctor, who practiced in the field of medical science. It was a physician's duty to save the lives of ailing patients, while at the same time preserving the life of healthy patients. (TOS: "The Enterprise Incident"; VOY: "Tuvix", "Retrospect", "Survival Instinct"; ENT: "Fortunate Son", "Regeneration")
In 1986, James T. Kirk, Gillian Taylor and Leonard McCoy masqueraded as 20th century physicians to gain access to Pavel Chekov at Mercy Hospital. Taylor later switched tactics and pretended to be the patient of the other two. (Star Trek IV: The Voyage Home)
As a physician, Beverly Crusher explained that "it's often my job to give people unpleasant news, to tell them they need surgery, or they can't have children, or that they might be facing a difficult illness." (TNG: "All Good Things...")