Simply for my own knowledge, I took
@azygous 's advice and looked up "hypericum safe for chickens". I find it interesting that hypericum is St. John's Wort, because I've previously read that St. John's Wort can be toxic to chickens. However, though I didn't research the issue in depth, St. John's Wort is anti-viral, which always always catches my interest since antibiotics are ineffective on viruses. Though I only briefly researched, there IS evidence that hypericum could be worth a try when a flock carries viral diseases, and if my flock carried a viral disease(s), I would do further research. Depending on what else I learned, I would be open to giving hypericum a try.
https://poultrydvm.com/supplement/st-johns-wort
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3384280/