Okay... this is my philosophy, so you have to take it at that. But....
I don't ever treat with a medication unless I know what I'm dealing with and a specific medication is indicated. It doesn't cost much to take a dropping sample in if you suspect worms or something like cocci. Treating with medications will make their system weaker, not stronger. Even if it is treating for the correct diagnosis, it takes some recovery after a medication to restore the system to health.
If you're just "taking a stab in the dark" your medication may be the "straw that breaks the camel's back" so to speak, as it ads another stressor to the system.
Then... if you do have an illness, the focus of "NATURAL CHICKEN KEEPING" is PREVENTION. If it's just a single bird with issues, and you're using natural husbandry, it's probably a bird that is weak in some respect. But always take a look at issues that may CAUSE illness or problems so that you can make healthy changes for prevention in the future