The prototypical antimalarial agent with a mechanism that is not well understood. It has also been used to treat rheumatoid arthritis, systemic lupus erythematosus, and in the systemic therapy of amebic liver abscesses. In March 2020, FDA issued an emergency use authorization (EUA) for hydroxychloroquine and chloroquine in the treatment of COVID-10. EUA was revoked in June 2020. Data from various published randomized, controlled clinical trials and retrospective, cohort studies have not substantiated initial reports of efficacy of 4-aminoquinoline antimalarials for treatment of COVID-19.