This is why the supply chain transparency in healthcare will be a great means of blatantly revealing unnecessary, deadly, and highly profitable over-prescription.
I assume you live in the United States? I see this kind of argument a lot, people complaining about doctors being "bought" by pharmaceutical companies. And while this is a large problem in the US, it isn't in most other developed nations. If you compare against the UK for example, doctors are given no financial incentive whatsoever for using or prescribing a particular drug. In many countries unnecessary prescribing is actually actively discouraged, with guidelines to follow and even punishments for doctors who hand out too many prescriptions.
A doctor should not have any mistake, and if ever, that shouldn't be kept as a lie.
That's an unreasonable expectation to have, I'm afraid. Everybody makes mistakes. It doesn't matter how trained you are, how experienced you are, how skillful you are. You can do something flawlessly a million times, and still make a mistake on the millionth-and-first time. In medicine there are countless checks, guidelines, checklists, routines, etc. designed to minimize mistakes. Obviously if mistakes happen, they need to be discussed openly and honestly and learned from, but you can never say there will be no mistakes. Mistakes are human nature.
To answer the broader question, of course doctors lie. Everybody lies. The differentiation to make is if the lie is ethical or unethical. Lying about medical advice or mistakes is obviously unethical, and should not happen and should be punished when it does. What about a patient involved in a road traffic collision, assault, shooting, or any other major trauma who was brought in and died in the ER or on the operating table from their injuries. What if the mother asks "Did they suffer?" or "Were they in pain?" I've lied in that situation several times. Is that ethical?