Hill's Prescription Diet cat food is generally well-tolerated and does not typically cause significant side effects when used as directed and under the guidance of a veterinarian. However, individual cats may react differently to any type of food, including prescription diets. Some cats may experience mild digestive upset or gastrointestinal changes during the transition period when switching to a new diet, including Hill's Prescription Diet. This can include symptoms such as loose stools, diarrhea, or occasional vomiting. These symptoms are usually temporary and resolve as the cat's digestive system adapts to the new food. In rare cases, cats may exhibit side effects such as loss of appetite, increased thirst, increased urination, excessive drooling, or weight loss. These side effects can occur due to various factors, including the cat's individual sensitivity or underlying health conditions. If any of these side effects are persistent, severe, or concerning, consult with your veterinarian for proper evaluation and guidance.