Hippocratic Oath
The Hippocratic Oath was an oath of guidelines and ethics sworn to by Earth physicians, devised by Hippocrates.

In 2152, when explaining the difference between Denobulan and Human medical ethics, Dr. Phlox stated "Hippocrates wasn't Denobulan". ()

The quote from the 's dedication plaque was the first part of the Hippocratic Oath: 
"I swear by Apollo the healer, by Aesculapius, by Health and all the powers of healing… " ()

The oath was included in the EMH programming. When given the opportunity to kill Unferth in the holodeck, The Doctor told him that the only reason that he wasn't going to kill him was because he had "taken an oath to do no harm." () He would later give this as the reason he could not perform the procedure to separate Tuvix in 2372. ()

In 2373, The Doctor recited to himself a version of the introduction to the oath which went as follows: 
"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." ()

In 2375, The Doctor, acting in his role as chief medical officer of , visited a holographic program he created of the Cardassian exobiologist Crell Moset to inform him that he had decided to delete his program and all related research due to ethical concerns. In response to this, the hologram stated that to do so would be to violate the first oath he took as a physician: "Do no harm." The Doctor, recalling the atrocities committed by the real-life Moset, told him that he had no right to say those words, and ignoring a final argument, proceeded with his decision. () 

He also turned down Qatai's offer to go hunting, stating that his program required him to do no harm. ()

While the oath required a doctor to do no harm, the specifics were sometimes open to interpretation depending on the wishes of the patient and a balance of consideration between physical and mental harm. In 2366, the Doctor faced a situation involving three former Borg drones who had been separated from the Borg Collective but were still linked in such a way that they could hear each other's thoughts. While it was possible to disconnect this link, doing so would mean that they only had a couple weeks to live, but the alternative was to return them to the Borg Collective. The Doctor was troubled by the possibility of taking an action that would result in their deaths. Seven of Nine, however, convinced him that to return to them the Borg would be doing an even greater harm, that survival was insufficient in the face of allowing them to have individuality. ()

In 2377, when his program was stolen by Gar and sold to Chellick, the Jye administrator of a floating hospital on the Dinaali homeworld, The Doctor, activated as Gar and Chellick negotiated over his price, angrily refused to provide his services to "common thieves" – but when victims of a mining accident were brought in seconds later, The Doctor, unable to simply stand and watch, began to treat a seriously injured miner, informing a surprised Chellick that, fortunately for the patient, he was programmed to obey the Hippocratic Oath. ()

Certain Malcorian physicians swear to an oath similar to the Hippocratic Oath. Berel specifically states "I have sworn an oath to do no harm. And I will not." ()

As of at least 2399, the EMH program contained Hippocratic coding to enforce this oath. ()

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