I know HN is place where anecdotes are not appreciated but here is one nonetheless.
I just caught flu a few days ago and my dad being my dad kept thrusting acetaminophen tablets to me (His way of showing love/care) and I relented after 24 hours of suffering with cold + fever + body aches.
I am 100% convinced that acetaminophen impaired my ability to work with tasks that required deep thinking. e.g: refactoring a feature that is spread across multiple services/repos.