Substance P is present in numerous organs (salivary glands, trachea, pancreas, kidneys, bladder and prostate) and in various parts of the central and peripheral nervous system, notably substantia nigra, hypothalamus, pineal body and dorsal horn of the spinal cord. It is a potent stimulant of salivary secretion and intestinal motility, a vasodilator in muscles and fatty tissues and an inhibitor of insulin release. Its main role, however, lies in the transmission of pain, where it seems to act as neuromodulator. Released when nociceptive fibers are activated at the same time as the fast-acting neuromediator, it enhances and prolongs the effects of the latter. Opiates inhibit its release. In addition, substance P is present in the excitatory neurones of the corpus striatum-substantia nigra pathway, which also has GABA-containing inhibitory neurones, and this pathway is known to modulate the dopaminergic nigra-striatum pathway. The global function of substance P, therefore, seems to keep the central nervous system in a state of alert through activation of the cerebral cortex and assistance in the transmission of pain.
P物质存在于众多器官（唾液腺、气管、胰腺、肾脏、膀胱和前列腺）以及中枢和外周神经系统的各个部位，尤其是黑质、下丘脑、松果体和脊髓背角。它是唾液分泌和肠道蠕动的强效刺激物，是肌肉和脂肪组织中的血管扩张剂，也是胰岛素释放的抑制剂。然而，它的主要作用在于疼痛传递，似乎在其中充当神经调节剂。当伤害性纤维与快速起效的神经介质同时被激活时释放，它会增强并延长后者的作用。阿片类药物会抑制其释放。此外，P物质存在于纹状体 - 黑质通路的兴奋性神经元中，该通路也含有γ-氨基丁酸（GABA）的抑制性神经元，并且已知该通路会调节多巴胺能黑质 - 纹状体通路。因此，P物质的整体功能似乎是通过激活大脑皮层并协助疼痛传递，使中枢神经系统保持警觉状态。
