Antihelminthic drugs are medicines that rid the body of parasitic worms. People can become infected with parasitic worms in a number of ways. The eggs of pinworms, for example, can be transferred from person to person through contaminated food, drinking glasses, clothing, or linens. Tapeworms and roundworms may enter the body when people eat undercooked meat or fish. The worms then live inside the body and may go unnoticed if they cause no troublesome symptoms. However, if they multiply rapidly or invade a vital organ, they can cause serious and sometimes life-threatening problems. The body has no natural means of getting rid of parasitic worms, but antihelminthic drugs do the job very well. Some kill the worms on contact. Others starve or paralyze the worms, which then pass out of the body in the feces.

Each type of antihelminthic drug is effective against particular kinds of...