Octopamine (OA), also known as para-octopamine and norsynephrine among synonyms, is an organic chemical closely related to norepinephrine, and synthesized biologically by a homologous pathway.

[9] Octopamine was first discovered by Italian scientist Vittorio Erspamer in 1948[11] in the salivary glands of the octopus and has since been found to act as a neurotransmitter, neurohormone and neuromodulator in invertebrates.

[23] In the nematode, octopamine is found in high concentrations in adults, decreasing egg-laying and pharyngeal pumping behaviors with an antagonistic effect to serotonin.

[25] In insects, octopamine is released by a select number of neurons, but acts broadly throughout the central brain, on all sense organs, and on several non-neuronal tissues.

[31][32] In larvae of the oriental armyworm, octopamine is immunologically beneficial, increasing survival rates in high-density populations.

The venom blocks octopamine receptors[34] and the cockroach fails to show normal escape responses, grooming itself excessively.

It may be responsible for the common side effect of orthostatic hypotension with these agents, though there is also evidence that it is actually mediated by increased levels of N-acetylserotonin.

Octopamine was positively identified in the urine samples of mammals such as humans, rats, and rabbits treated with monoamine oxidase inhibitors.

[12] Octopamine has been sold under trade names such as Epirenor, Norden, and Norfen for use in medicine as a sympathomimetic drug, available by prescription.

[60] It has been studied as an antihypotensive agent and has been shown to increase blood pressure when administered intravenously, intramuscularly, and buccally at sufficiently high doses, whereas oral administration was ineffective.

[63][64][65] The octopamine receptor is a target of insecticides, as its blockage leads to decreased cyclic adenosine monophosphate (cAMP) levels.

Essential oils can have such a neuro-insecticidal effect,[66] and this octopamine-receptor mechanism is naturally utilized by plants with active insecticidal phytochemicals.

[68][69] Octopamine binds to its respective G-protein coupled receptors (GPCRs) to initiate a cell signal transduction pathway.