Hydroxychloroquine sulfate is primarily used in the treatment of malaria, particularly for cases caused by Plasmodium vivax, Plasmodium malariae, Plasmodium ovale, and sensitive strains of Plasmodium falciparum. It is also employed in the prophylaxis of malaria for individuals traveling to endemic regions. Beyond its antimalarial properties, it is widely prescribed for autoimmune conditions such as rheumatoid arthritis and systemic lupus erythematosus, where it helps reduce inflammation and modulate immune responses. Additionally, it has been explored for its potential antiviral effects, though its efficacy in this area remains controversial and subject to ongoing research.