Do you have an actual instance of something like that happening? I'm not saying it never has. An MD ought to know his/her patients well enough to judge what kind of idiocy they're likely to go off and try.

One thing where I do not have a link is but I recall it happening is: quackery is impossible to kill with research. Someone does a double- blind study showing that peach pits are worthless against cancer, and the peach pit "doctors" just say "studied by legitimate science!" or "more research is needed!"