No, the Corid will not harm them if it isn't Coccidiosis.
Everyone,
Corid doesn't harm them, yet, it can (not will, can) create unwanted side effects. For example, it can create a reduced immune system which can let other things (like dormant Marek's) get a foot hold. It depletes Vitamins A and K during the dosage period of 5 days. After that 5 days, many references suggest a vitamin supplement. I'm not suggesting that the original person posting not use Corid, just sharing what I know. Most of this information came from "The Chicken Health Handbook" by Gail Daerow.
I share this because I may (again, who can say for sure without a necropsy) have experienced this myself, so now I'm more cautious prior to administering drugs as my first action. My coop flooded during a monster storm (which I have since fixed by digging ditches). Then, I got what I think might have been cocci so I treated with Corid. Almost within days, I had one chick come down with something i never figured out what it was, but the symptoms were lethargy, green/yellow poo, not eating or drinking. This lasted for 4 days and then that chicken recovered. Then, during that time the chicken with green poo was sick, a second one had an outbreak of Marek's (classic Marek's symptoms). I culled that chicken. Everyone has been healthy since which was 3 weeks ago. Then, this morning when cleaning up last night's poo, I noticed I have 1 chicken with bright red bloody poo. I believe I've narrowed it down to one chicken that got into my compost pile and ate about several (maybe 4) cherry pits yesterday. But, he's not exhibiting any other symptoms, just happily going about his day. None of the others are acting sick in any way either. So... I'm trying to wait just maybe another day and see before treating the flock for cocci with the Corid.
My situation is different as all our situations are unique, but thought I'd share this in case it helps others. Treating the chickens with drugs is often the right thing to do but it also can cause them various stresses and reduced immunity to other things. Mine are just at the point of lay so they're already stressed by the maturing process, mating, egg laying, etc. Maybe I'll regret not treating with Corid right away but last time, I think I reacted too quickly.
Just sharing my story and perspective, in case it's helpful to others.
Guppy
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