I think most of the time vets are concerned that the cat guardian won't make sure their cat eats every bit of the food the pill has been mixed into. It should be crushed into a fine powder (I use two teaspoons) and then mixed in with the food so that it's well distributed. Even using the most favorite food of each cat, I've only had about 25% success with putting medication in food. And, of course, some pills are very bitter and so harder to mask in food.