No. Dr. Jones' Ultimate Feline Health Formula is not a pharmaceutical drug - it is a naturally derived health supplement. All ingredients are either in their natural form or they are derived from a natural source - there will be no side effects unless your cat has a pre-existing sensitivity to a particular ingredient.

Point to note - when some cats start on Dr. Jones' Ultimate Feline Health Formula, they can go through a bout of diarrhea and/or vomiting. This is quite normal when just starting on a concentrated health supplement - for both humans and pets! This is referred to as "going through a nutritional boost", but it shouldn't last. If it is continuous, just go off the supplement for a few days until things "stabilize", then slowly reintroduce it into the food again in smaller amounts, then work up to the recommended dosage.