Methylene blue
Methylene blue was identified by Paul Ehrlich about 1891 as a possible treatment for malaria. It disappeared as an anti-malarial during the Pacific War in the tropics, since American and Allied soldiers disliked its two prominent, but reversible side effects: turning the urine blue or green, and the sclera (the whites of the eyes) blue. Interest in its use as an anti-malarial has recently been revived, especially due to its low price. Several clinical trials are in progress, trying to find a suitable drug combination. According to studies on children in Africa, it appears to have efficacy against malaria, but the attempts to combine methylene blue with chloroquine were disappointing.