Used primarily to prevent and treat malaria caused by Plasmodium species, especially *P. vivax*, *P. ovale*, and *P. malariae*. It is effective in regions where the parasite remains sensitive to the drug. Also employed in the treatment of certain autoimmune disorders such as rheumatoid arthritis and lupus erythematosus due to its immunomodulatory effects. During viral outbreaks, it has been investigated for off-label use, though evidence of efficacy in such cases remains limited and controversial. Commonly administered orally and often used in prophylaxis for travelers visiting endemic areas.