Zelda is probably eating all the extra food to try and get rid of the taste of the meds, so she may naturally lose the weight when she is done the medication.
I wish that were the case, but she was over-eating even before she got the meds! Anyway, before I left for work this morning, I put 1/2 cup of food in her bowl (she'll get another 1/2 cup this afternoon), and in about 30 minutes her bowl was empty!