Science, being a human endeavor, is imperfect.
The following is a long list of "miracle drugs" that have been withdrawn from market:
https://en.wikipedia.org/wiki/List_of_withdrawn_drugs
"Where risks or harms is the reason for withdrawal, this will usually have been prompted by unexpected adverse effects that were not detected during Phase III clinical trials, i.e. they were only made apparent from postmarketing surveillance data collected from the wider community over longer periods of time." (article above)
https://www.drugsdb.com/blog/fda-app...om-market.html
Certainly if a presidential candidate is entitled to change his mind on major issues, the FDA is, too. Of course, the entire process of reversal is quite a bit more serious when it comes to a federal agency in charge of the welfare of the country.
Let's start with a very sobering fact: More Americans die from adverse effects of prescription drug medications than from illegal drugs. (Ed note: All hail science!)
"That means that the agency overseeing prescription medications carries a heavy burden, the burden of human lives." (article above)