While I agree with the premise that people with years of education and experience in their specialized fields will generally know more than you, I have quite a bit of personal experience that there is a lot of contradictions and discrepancies when it comes to the medical field.

I recently leveraged my grassroots lobby legal expertise into a significant position in a major pharmaceutical company (switching sides, betrayal, or perhaps double agency call it what you will) and you would not believe the bureaucratic behavior between not only the government but hospitals and clinics as well. NDA's prevent me from disclosing specifics, but we're talking quotas, blacklisting, and other shady stuff here. This means the doctor may fully well know what the root cause of your problem of thinning hair will be, but s/he may put you onto a prescription for fildeafil for the rest of your life because it is more profitable. Not saying that this behavior is good or bad, it is what it is.

Stay informed, and explore your options is all I can say.