German Shepherd dog

The medicine likely does not affect his sense of smell, but it does affect his overall capacity to think and this is probably what is being observed. The good news is that in time he probably will adjust to the medicine and may do much better and be more normal and able to think more clearly. Unless the epilepsy is due to a tumor or other specific anomaly in the part of the brain that controls the sense of smell, this too is not likely to be at issue. The medicines will also affect his appetite and that could make things more difficult if his normal reward has been food for tracking.

I'm not sure about a dogs ability to smell, but I have temporal lobe epilepsy and the sense of smell is situated in the temporal lobe of the brain.  In my case when I have a seizure my sense of smell is incredibly heightened.  So maybe the reverse can happen too.