Quinine malaria drug, molecular model. Quinine is a drug used to treat malaria. It is obtained from the bark of the cinchona tree (Cinchona sp.), which is native to South America. Quinine has been used to treat malaria for over 300 years. Malaria is a tropical disease caused by the presence of Plasmodium sp. protozoa in the blood. Quinine interferes with the parasite's ability to digest haemoglobin and so starves them. Quinine's chemical formula is C20H24N2O2. Atoms are represented as spheres and are colour-coded: carbon (C, grey), hydrogen (H, turquoise), nitrogen (N, blue) and oxygen (O, red).