- Advantage flea killer can cause the pet to have a rash where the flea killer was put onto the pet's skin.
- Be careful to keep the product away from the pet's eyes, or serious eye irritations can occur. Also, do not touch your own eyes or skin until you've washed your hands thoroughly after applying the product.
- The main ingredient, imadacloprid, has been linked to serious problems such as organ damage. Although not proven to be dangerous in Advantage, this ingredient might be linked to thyroid lesions, increased organ weight and increased cholesterol levels in laboratory animals.
- Carcinogenic effects have not been proven, but studies with laboratory animals show that this could be a possible side effect. Common ailments include issues with fertility and bone marrow, and sometimes even affect the animal's offspring.
- There is evidence that imadacloprid affects the neurotoxin system to cause problems such as labored breathing and muscle weakness.
