@partha Many physicians still hold beliefs despite the existence of clear evidence that they are incorrect.
These long-held pieces of dogma – or "medical myths" – were engraved during training or early in the careers of many physicians, and are difficult to overcome.
The myths persist because medical professionals get taught one way in training, given a 'truth' or 'This is the way we do it,' and then do not ever rethink, 'Is it true?' Studies pop up to question conventional wisdom, but unless the studies get highly publicized, they aren't noticed.
Three of what considered to be some of the some of the medical myths that are in greatest need of being dispelled.

Shellfish Allergy and Radiocontrast
A myth persists that people with a shellfish allergy could have an allergic reaction when a contrast agent is used for a scan. This belief arose, because fish and shellfish contain iodine, and allergic reactions to seafood are fairly common, and contrast agents contain iodine, too.
The belief is widespread, with 65% of radiologists and 88.9% of interventional cardiologists saying they ask about seafood or shellfish allergies before administering contrast. And a third of radiologists and 50% of cardiologists said they would withhold contrast media or recommend a premedication for patients with such an allergy.

But the belief makes no sense, Iodine is present in many other foods, including milk and bread, and allergies to shellfish are because of parvalbumin protein and tropomyosins, not iodine.

Colonoscopy Dogma
It's been long believed that people need to be on a clear, liquid diet for 1 or 2 days and need to drink a bowel-prep liquid before a colonoscopy.
But the evidence shows this isn't necessary, he said.

A 2020 study found that a low-residual diet, allowing foods such as meat, eggs, dairy, and bread, were comparable to the clear liquid diet in terms of bowel prep and detection of polyps during the exam. The patients on the low-residual diet had less nausea, less vomiting, and less hunger, and expressed more willingness to have a repeat colonoscopy.
Metronidazole and Alcohol
There is a belief that patients shouldn't drink alcohol if they are taking metronidazole, because of concerns about nausea, vomiting, flushing and other symptoms – also known as a disulfiram like reaction.

Case reports have been published, but the cases were presented as though a metronidazole-ethanol reaction was an established fact, and the authors didn't provide evidence to justify this.

But it's been shown in rat models that metronidazole can increase levels of acetaldehyde, the trigger of symptoms, in the colon, but not in the blood. And in a small placebo-controlled, randomized trial, six people were given metronidazole and ethanol and, after regular blood testing, no difference was seen in acetaldehyde blood levels, vital signs, or symptoms.The Centers for Disease Control and Prevention has said that avoiding alcohol while taking metronidazole is unnecessary.

Sinus Headaches
Contrary to common belief, headaches thought to be "sinus headaches" are usually migraine headaches. In one study, 2,991 patients with six headaches in the previous 6 months were self-diagnosed or were physician-diagnosed with sinus headaches. But 88% of these headaches met the International Headache Society criteria for migraine headache.

The clinicians should reconsider the evidence regularly when deciding how to treat their patients, and not rely on bits of dogma.