History of the Hippocratic Oath

Some points:

...the tinkering with Hippocrates' oath began soon after its first utterance and generally reflected the changing values, customs, and beliefs associated with the ethical practice of medicine. Consequently, there are stark differences between the promises made in the original version and the oaths sworn today.

We no longer pledge allegiance to the ancient Greek gods Apollo, Asclepius, Hygieia, and Panaceia.

There are two highly controversial vows in the original Hippocratic Oath: the pledges never to participate in euthanasia and abortion.

Hippocratic physicians represented only a small minority of all self-proclaimed healers... We have fairly reliable historical documentation, however, that many ancient Greeks and Romans who were confronted with terminal illness preferred a quick, painless death by means of poison to letting nature take its course. Moreover, there were no laws in the ancient world against suicide, and it was not uncommon for physicians to recommend this option to a patient with an incurable disease.

Similarly, abortion, typically effected by means of a pessary that induced premature labor, was practiced in both ancient Greece and the Roman Empire. Many Christian revisions of the Hippocratic Oath, especially those written during the Middle Ages, prohibited all abortive procedures.

...the relevant sections are simply omitted in most oaths administered by U.S. medical schools. As of 1993, only 14% of such oaths prohibited euthanasia and only 8% prohibited abortion.