You'll need to slowly fade out the medicated over a period of time. Add a little nonmedicated with it each day while using a little less medicated. Do this daily until you are using just nonmedicated feed. I don't think the non medicated feed hurts them, with the exception that it does help prevent coccidiosis. Which if you have older chickens that they are with or will be going out with, they should have until they are a few weeks older. Or so I'm told. I use non-medicated myself from day one and all my birds are fine. I think it's owner's/user's discretion. We just try not to medicate at all, and we start at the begining with chick feed.