Am sure you can find plenty when you go down this rabbit hole but you can start here: https://twitter.com/us_fda/status/1429050070243192839
Astral Codex Ten has a great writeup on this, and a big controversial debate with the ivermectin crowd. It's pretty glorious, and I do recommend reading it in its entirety.
If you do want to call this a lie, I suppose I could see it. Someone claims something helps Covid, but it shouldn't, because it doesn't make sense, so instead of trusting the studies, they go out making a bold claim like this, that ivermectin is completely ineffective.
In any case, this does reduce trust in those agencies, when they ignore science and instead spout off politically-expedient dismissals of data.
But I wouldn't call it lying, really.
On Astral Codex Ten's piece, I assume you are talking about this one [0] The whole piece is such a doosie. Am almost sure 90%+ of the non-core audiences that landed on the page never scrolled to the end. If you are going to debunk a controversial subject, KISS. Not to say he didn't do a good job at poring through the numerous inconsistent data and studies carried out on the possibility of use of ivermectin for treatment. But am sure I came across some of his material on the interwebs.
Back to the source material of this post, FDA were completely malicious by tweeting that. Their linked post even goes to mention that taking ivermectin could be lethal for you.
What happens when the body whose sole job is to be the arbiter of truth and science regarding safety of drugs knowingly makes obviously dubious false verifiable claims? They are either knowingly participating in a lie or they are incompetent.
[0] https://astralcodexten.substack.com/p/ivermectin-much-more-t...
Turns out giving ivermectin (parasite killer) in a country where a lot of people have parasites is good public health policy. It's just butt stupid to use in a developed country like the US where ivermectin probably won't help people, but that doesn't stop people from taking horse dewormer in Florida :/.