Medical Myths Debunked: Common Knowledge Clinicians Need to Unlearn
Medical myths can undermine care by clinging to outdated practices. Many physicians still follow guidance learned during training—even when new evidence contradicts it. These persistent beliefs, often ingrained early, are what Dr. Douglas Paauw of the University of Washington calls “medical dogma”: habits reinforced by repetition rather than what the research shows.
Dr. Paauw is on a mission to help clinicians unlearn what no longer holds true, whether it's the belief that patients with pernicious anemia must get B12 shots or that flu vaccines cause flu-like illness.
Challenging these ingrained ideas isn’t about proving someone wrong—it’s about raising the standard of care. Progress requires unlearning as much as learning. Let’s unpack some of the most common medical myths and why they’ve persisted.
What Makes a Myth in Medicine?
Medical myths often begin as well-intentioned teachings passed down during the earliest stages of training. At that point, future physicians are absorbing massive amounts of information—much of it committed to memory without question. Even information that turns out to be outdated or incomplete can persist for decades simply because it was learned early and repeated often.
Changing those beliefs takes more than new data. It takes consistent exposure to current evidence-based learning. That’s why ongoing CME isn’t just a requirement—it’s a critical tool for correcting course and keeping clinical care aligned with the latest standards.
5 Common Medical Myths Debunked
Clinical habits can be difficult to break, regardless of whether they’re correct. Here are six common myths that continue to show up in practice, along with the evidence that disproves them.
You Can’t Absorb Vitamin B12 Orally if You Have Pernicious Anemia
“The teaching always was, if you can’t absorb it, you got to give it by injection,” Dr. Paauw says. But research dating back more than 60 years has shown otherwise: “Studies were done that showed that if you give enough oral B12, it’s well absorbed, and patients can normalize their B12 levels so they don’t need B12 shots.”
Even with widespread awareness among physicians, he estimates that “a third to half of the people who have B12 deficiency get B12 shots in the United States.”
The Flu Shot Can Give You the Flu
“Many times during the flu season, when we want to give flu vaccine … [patients] will say, ‘I don’t want that, because the last time I got a flu shot, I got the flu. It gave me the flu.’” Dr. Paauw points to two placebo-controlled studies that debunk this myth. “The only difference between getting a flu shot and getting the saline was your arm hurt a little more if you got the flu shot. That was the only difference.”
Another trial confirmed the same outcome, he says: “Absolutely no difference in flu-like symptoms between getting a saltwater injection or the flu vaccine.”
Colonoscopies Require a Clear Liquid Diet and a Gallon of Laxative
Traditional colonoscopy prep regimens often involve a clear liquid diet for 24 hours and a full gallon of bowel prep solution—protocols that deter patients from screening. But newer studies show there’s a better way. “There are many lower-volume bowel preps on the market now … and those options are just as good or better than GoLYTELY,” says Dr. Paauw.
A low-residue diet—featuring pasta, rice, and even ice cream—performs as well or better than clear liquids, and smaller-volume prep options are now widely available. For patients, it’s a more humane and manageable approach.
Epinephrine Should Never Be Used in Fingers or Toes
Medical trainees have long been taught that injecting epinephrine into end-arterial areas like fingers or toes could cause necrosis. That teaching, Dr. Paauw says, is outdated. “There was a very nice study done about 15 years ago that showed that, in hand surgery practices encompassing over 3,000 patients where they used lidocaine with epinephrine, they had zero complications.”
Controlled studies and surgical experience support the safety of lidocaine with epinephrine for hand procedures, with one caveat. Patients with known ischemic conditions should still be approached cautiously. For most patients, however, this method reduces bleeding and makes procedures easier to perform.
Mixing Alcohol with Metronidazole Is Dangerous
The warning about combining alcohol with metronidazole has been in textbooks for decades, but solid evidence for it is thin. “There really isn’t this drug interaction between metronidazole and alcohol,” Dr. Paauw explains. In a study of 12 medical students, each volunteer was given a daily dose of ethanol. Half of the participants also received metronidazole, “and half of them were given a placebo … and they found no difference.”
A broader emergency room study confirmed this finding, he adds: “They found no increased risk of having one of these reactions … in patients who were taking both alcohol and metronidazole versus equal amount of alcohol alone.”
While both substances can cause nausea individually, no true interaction has been consistently demonstrated. Even the CDC has dismissed the concern in its STI treatment guidelines. While heavy drinking is never advised, patients don’t need to avoid a glass of wine or toast at a wedding during a metronidazole course.
Why These Myths Matter
Outdated medical beliefs cloud clinical judgment, leading to unnecessary treatments, poor patient adherence, and eroded trust. Whether it’s a patient refusing a flu shot out of fear or avoiding a colonoscopy because of an overly burdensome prep, these myths affect real decisions in practice. Left unchallenged, they become embedded in routine, passed from one clinician to the next.
“We have to keep an open mind,” says Dr. Paauw. “We have to let go of dogma sometimes.” Staying current with evidence-based updates is a commitment to delivering better care, building stronger patient relationships, and making room for new and more effective ways to treat and communicate.
How to Stay Current—and Leave Medical Myths Behind
Most medical myths persist because they’re familiar. “The real danger,” Dr. Paauw says, “is you get busy and then a month goes by, two months go by … and you haven’t really done anything to learn anything new.” Staying current requires more than intention; it takes a plan.
Dr. Paauw encourages clinicians to find reliable, recurring sources of education that fit their learning style and schedule. “Everybody has to find something they check in with every month that will keep them current.” His go-to recommendations include Oakstone’s ACP MKSAP Audio Companion, and the Curbsiders podcast.
Unlearning outdated practices is just as important as acquiring new knowledge. With the right tools, clinicians can stay sharp, challenge old assumptions, and provide care that’s both current and compassionate. Explore Oakstone’s CME resources for efficient ways to stay informed and update your practice with confidence.