Chloroquine is a medication primarily used to prevent and treat malaria, a disease caused by parasites transmitted through mosquito bites. It works by interfering with the growth of the parasites in the red blood cells of the host. Chloroquine is also used to treat certain autoimmune diseases, such as lupus and rheumatoid arthritis, due to its anti-inflammatory properties. Originally developed in the 1930s, chloroquine has been a key drug in the fight against malaria, especially in regions where the disease is prevalent. However, the emergence of drug-resistant strains of the malaria parasite has led to a decline in its effectiveness, prompting the search for alternative treatments and preventive measures.