Popular flea and tick pills given to millions of dogs and cats may be quietly harming the environment. Credit: Shutterstock A study published in Environmental Toxicology and Chemistry by Oxford University Press reports that widely used flea and tick treatments for dogs and cats may pose a serious threat to insects in the natural environment. Isoxazoline drugs are a relatively new class of antiparasitic medications prescribed by veterinarians around the world to protect pets from fleas and ticks.