Chloroquine is a pharmaceutical used in the treatment of malaria. It has largely replaced quinine for this purpose. It received limited use shortly after it's discovery because it was thought it was very toxic to humans. However, clinical trials in the 1940s showed it to be superior to its predecessor and it was commonly used to prevent the contraction of the disease. It can also be used to treat some autoimmune disorders as it suppresses the immune system. It is also under investigation for the treatment of AIDS and cancer.