Wormwood is one of the most popular herbal remedies for getting rid of roundworms, tapeworms, pinworms, and threadworms that may infect the intestinal tract of your cat. It contains sesquiterpene lactones, isothujone, and thujone, which are known for effectively weakening and killing parasites. When it comes to using wormwood, however, you should work with a holistic veterinarian who knows the right amount to use for your particular pet.