Hydroxychloroquine is a medication that is commonly used to treat malaria, lupus, and rheumatoid arthritis. It works by reducing inflammation and suppressing the immune system. Some studies have suggested that it may also be effective in treating COVID-19, but its effectiveness for this purpose is still under investigation. Hydroxychloroquine should only be used under the guidance of a healthcare professional, as it can have serious side effects if used improperly.