The Centers for Disease Control and Prevention is warning people about the danger of using non-pharmaceutical chloroquine phosphate to prevent or treat COVID-19. The agency put out a health advisory Saturday, explaining that non-pharmaceutical chloroquine phosphate is a chemical used in home aquariums. "Clinicians should advise patients and the public that chloroquine, and the related compound hydroxychloroquine, should be used only under the supervision of a healthcare provider as prescribed medications," the advisory reads.