In the 20th century, toxicology testing became important. In the 19th century, laws about drugs were less strict. Drugs did not have to be checked for safety. But in 1937, a drug called Elixir Sulfanilamide killed more than 100 people. They caused great and long lasting pain, vomiting, and fits. After that, the U.S. congress made laws that said that drugs had to be tested on animals before they could be sold. Other countries passed similar laws.