Nicotine was observed to fight gastrointestinal parasites.

An excerpt from the article 15 facts about nicotine

Pygmies are said to be the most addicted to nicotine. In the Aka tribe living in central Africa, almost 95 percent of men are smokers. Pygmies earn an average of 50 cents a day, half of which they spend on tobacco. Canadian anthropologist Edward Hagen from Washington State University studied their addiction to nicotine and concluded that by smoking tobacco, Pygmies naturally fight against gastrointestinal parasites, tapeworms, and roundworms.