Mixed feelings about this, I have used chick starter medicated with no problems. It even talks about medicated in Storey's Guide about using it (with other options too) which is like the bible for duck raising. I use the starter feed and now on the flock raiser and will start using layer feed mixed with it, all purina brand. When it came to medicated the ducklings I did not use medicated with were my problem ones but could of been bad genetics, niacin deficient as well. I supplemented niacin in their water, I still give them some now (not an expert on it). The ducklings I have used with medicated feed, I had no problems what so ever. If there is a reason not for ducks to be medicated please educate me, from the posts I have seen there is no proof against it.