Anthelmintics are used to treat people who are infected by helminths a condition called helminthiasis. Anthelmintic drugs are also used to treat infected animals. Anthelmintics are a group of Anthelmintic medication that expel parasitic worms (helminths). and other internal parasites from the body by either stunning or killing them and without causing significant damage to the host. anthelmintic definition, side effects of anthelmintic drugs and more.