I can give some hare-raising examples[0] but for obvious reasons... The one I can give is it was known that docs who prescribed this to multiple patients and saw an apparent improvement the attributed to the new drug, would switch the patients on the old drug to the new and not inform us. Obviously they couldn't or they'd invalidate the trial and they knew it. And it was done entirely with the patient's best interests at heart. Docs care about their lives.
That may have been rare and a flaw in the trial protocol, but much worse stuff was done via utter incompetence. And I mean including at the top of these giant drug companies. Run by idiots, really.
Wider lesson: just cos you hand over a process to a third party does not mean it's going to be done right.
[0] tribute to the thread elsewhere