Hydroxychloroquine drug for malaria, molecular model. Hydroxychloroquine is a medication for the prevention and treatment of malaria. The drug is also used for rheumatoid arthritis, lupus and porphyria. Contrary to widespread disinformation, clinical trials show that hydroxychloroquine is ineffective for Covid-19. are colour-coded: carbon is black; hydrogen is white; chlorine is green, nitrogen is blue; oxygen is red.