Since glycans play an important role in intercellular interactions and protein, they serve as viable targets for various therapeutic interactions. Multiple current therapeutics aim to take advantage of their role in signaling pathways, and target their biosynthesis or engineer related glycoproteins. These interactions can be controlled by encouraging or inhibiting the presence of those glycans that mediate signaling, which is the mechanism of action for a number of extant drugs, including heparin, erythropoietin, the antivirals oseltamivir and zanamivir, and the Hib vaccine. Furthermore, the glycans themselves can serve as drugs and there is ongoing research and development to engineer more effective ones.