treats

c is a substance that treats d if c is a material entity (such as a small molecule or compound) and d is a pathological process, phenotype or disease, and c is capable of some activity that negative regulates or decreases the magnitude of d.

http://purl.obolibrary.org/obo/ro/docs/causal-relations

https://code.google.com/p/obo-relations/issues/detail?id=46