Here, this is copied from another thread and I found this same answer in multiple places. The ducklings raised on the medicated started were just fine. If the active ingredient is amprolium, then it's safe.
"Amprolium is absolutely safe for ducks. It was the old medicated chick starter of many decades ago that ducklings couldn't have. Information seems to be lagging about 40 years behind reality. Old wives tales get repeated over and over just like they are the truth."
"Amprolium is absolutely safe for ducks. It was the old medicated chick starter of many decades ago that ducklings couldn't have. Information seems to be lagging about 40 years behind reality. Old wives tales get repeated over and over just like they are the truth."