You want the best for your pets and when they're sick, sometimes that means buying expensive prescription pet food. Because that food requires a prescription from your vet, it's reasonable to think you're buying medically necessary, pure, high-quality active ingredients to make your pet well. What you’re actually getting may be a hard pill to swallow. “There is no medicine in prescription pet foods. There's nothing ‘prescription’ in the food at all,” said Dr. Karen Becker.