No, Trifexis does not work on tapeworms. The active ingredients in Trifexis are efficient against adult roundworms, adult hookworms, and adult whipworms. However, Trifexis has an indirect effect on tapeworms as it controls fleas that are tapeworm (Dipylidium caninum) hosts. Fleas are not the only source of tapeworm infections for dogs. Therefore, to ensure your dog is fully protected, you need a preventative medication with Praziquantel as an active ingredient.