Yes. You should not be using it for long. Healthy fish can handle this. If you are using prazi along with copper or hypo or other treatments for long periods of time, then all of these can be bad since they suppress appetite too.
Fro. What ive seen its not as bad as people claim. I neverhad a fish stop eating completely because of it. I even feed food soaked in prazi, fish will spit a few rime but still eat when hungry.