S-Hydroxychloroquine is primarily used in the treatment and prevention of malaria, particularly in regions where the malaria parasite has developed resistance to other medications. It works by interfering with the growth and survival of the parasite in the red blood cells. Additionally, it is employed in the management of autoimmune diseases such as rheumatoid arthritis and lupus erythematosus. In these conditions, it helps to reduce inflammation and modulate the immune response, alleviating symptoms like joint pain, swelling, and skin rashes. During the COVID-19 pandemic, it was explored as a potential treatment, though its efficacy and safety for this purpose remain controversial and not widely recommended.