Octopamine (molecular formula C8H11NO2) is an organic chemical closely related to norepinephrine. In many types of invertebrates it functions as an important neurotransmitter and hormone, but in the human body it normally exists only at trace levels and has no known function. Because it shares some of the actions of norepinephrine, octopamine has been sold under trade names such as Epirenor, Norden, and Norfen for use as a sympathomimetic drug, available by prescription. Very little information exists concerning its clinical usefulness or safety.