Dr. Mehmet Oz is fighting back against prominent physicians who recently called for Columbia University to remove him from their faculty.
The Dr. Oz Show host is a professor of surgery at the Ivy League school, and holds the surgery department's vice chairmanship at the medical school.
"Dr. Oz has repeatedly shown disdain for science and for evidence-based medicine, as well as baseless and relentless opposition to the genetic engineering of food crops," read a letter addressed to Dr. Lee Goldman, Columbia's Dean of the Faculties of Health Sciences and Medicine. "Worst of all, he has manifested an egregious lack of integrity by promoting quack treatments and cures in the interest of personal financial gain."
The letter was signed by 10 different doctors.
On Thursday's episode of his hit ABC show, Dr. Oz addressed his critics head-on.
"I know I've irritated some potential allies in our quest to make America healthy," he said. "No matter our disagreements, freedom of speech is the most fundamental right we have as Americans -- and these 10 doctors are trying to silence that right. So I vow to you right here, right now, we will not be silenced. We will not give in."
This isn't the first time Dr. Oz has had to defend himself. Last June he was grilled by Congress for using language like "miracle in a bottle" when mentioning products on his show. But he insisted that he does not endorse the products he discusses on his show.
But in a new interview with Stephanie Gosk airing on NBC Nightly News Thursday, the 54-year-old physician does admit to some regrets.
"There are segments that I made that I wish I could take back," he reflects. "If I could just go back in time, I would have never allowed those words to come out of my mouth, because it completely perverted the conversation I was having with America. But I can't take back those segments. They're stolen, they're gone, and they're all over the web."
That's not to say he's taking the new attack on him lightly.
He's set to further discuss the controversy with Matt Lauer on TODAY Friday morning and in a new op-ed for Time published Thursday, Dr. Oz went on the offensive, calling out some of the doctors who signed the letter for having their own conflicts of interest.
"The lead author, Henry I. Miller, appears to have a history as a pro-biotech scientist, and was mentioned in early tobacco-industry litigation as a potential ally to industry," he writes as an example. "He also furthered the battle in California to block GMO labeling -- a cause that I have been vocal about supporting."
In the passionate essay, Dr. Oz explains his exploration of "alternative medicine."
"My exploration of alternative medicine has never been intended to take the place of conventional medicine, but rather as additive," he stresses. "I have spent my entire career searching for ways to lessen the suffering of my patients. The best and safest paths have generally been the traditions of conventional medicine. They are tried and true, well-funded, and fast. But there are other routes to healing that offer wisdom as well, so I have been willing to explore alternative routes to healing and share any wisdom that can be gathered."
Watch the video below to see ET look into whether the Congressional hearings last year have affected Dr. Oz's credibility.