How Does Substance P Work? Mechanism of Action, Per the Research

The short answer

Substance P is a short neuropeptide released largely from sensory nerve endings and from several non-neuronal cell types. A biochemistry review described it as an 11-amino-acid member of the tachykinin family, encoded by the TAC1 gene, that exerts its effects primarily by binding the neurokinin-1 (NK-1) receptor, a G-protein-coupled receptor expressed on neurons, endothelium, smooth muscle and immune cells (PMID 32119470). Everything else described below, vasodilation, immune activation, pain amplification, itch, follows from that receptor interaction and the intracellular cascades it triggers.

This page is for educational purposes only and is not medical advice; consult a licensed physician before making any health decision. It summarises published mechanism literature and does not describe protocols, quantities or schedules, and no dosing information appears anywhere on this page because the cited papers are mechanistic rather than dose-finding work.

Step 1: Where substance P comes from

Gene, peptide and storage

The biochemistry review reported that substance P derives from the preprotachykinin-A (TAC1) gene, which also gives rise to other tachykinins, and that the mature peptide is stored in vesicles within primary afferent sensory neurons and released on stimulation (PMID 32119470). The same review noted that substance P is not confined to the nervous system; it described expression in and release from immune and inflammatory cells, which is the structural basis for the peptide being treated as a neuro-immune messenger rather than a purely neuronal transmitter (PMID 32119470).

Release triggers described in animal work

Sensory fibres expressing the capsaicin-sensitive TRPV1 channel are a principal source. In a mouse study, researchers reported that trigeminal TRPV1-expressing neurons formed the link by which sleep deficiency exacerbated periodontal inflammation, implicating peptide release from these sensory fibres as the effector arm of the circuit (PMID 40489620). That work was conducted in animals, and the authors framed it as a neuro-immune mechanism rather than a clinical finding (PMID 40489620).

Step 2: Receptor targets

Three mammalian tachykinin receptors exist, NK-1, NK-2 and NK-3, and the biochemistry review reported that substance P has highest affinity for NK-1 while still interacting with the other two at lower affinity (PMID 32119470). Because NK-1 is the dominant target, most pharmacological probes used in the literature are NK-1 receptor antagonists, and a review of NK-1 receptor antagonists in pruritus treated receptor blockade as the standard way to test whether a given effect is substance P-dependent (PMID 33675531).

Why receptor location matters

The same biochemistry review described NK-1 receptor expression across the central nervous system, peripheral neurons, vascular endothelium, smooth muscle and immune cells, which explains why a single peptide is discussed in literatures as different as emesis, mood, wound biology and inflammation (PMID 32119470). Tissue distribution, not peptide identity, drives which downstream physiology dominates in a given model.

Step 3: Signal transduction

The biochemistry review characterised NK-1 as a G-protein-coupled receptor, with ligand binding initiating intracellular second-messenger signalling and the downstream cellular responses associated with tachykinin activity (PMID 32119470). In practical terms, published work reads out this cascade through its consequences rather than the cascade itself: calcium-dependent transmitter release at central synapses, endothelial relaxation in vessels, degranulation in mast cells and cytokine transcription in immune cells.

A 2024 preclinical paper added an intracellular pathway that is less often discussed: researchers reported that substance P attenuated experimental colitis by suppressing inflammation and ferroptosis through the cGAS-STING signalling pathway (PMID 38725846). That study was conducted in laboratory models rather than patients, and it is a useful reminder that substance P signalling is not uniformly pro-inflammatory across every tissue and context (PMID 38725846).

Step 4: Downstream physiology, neurogenic inflammation

The best-characterised integrated output of substance P signalling is neurogenic inflammation: sensory nerve activation releases peptide into tissue, which acts on local vessels and immune cells to produce vasodilation, plasma extravasation and leukocyte recruitment. A 2025 mouse study provided a current example, reporting that tuft cells triggered neurogenic inflammation in the urethra through sensory-neuron crosstalk (PMID 41032411). The study was performed in animals and described an epithelial-to-neuronal signalling loop rather than a human disease mechanism (PMID 41032411).

Mast cells as an amplifier

Mast cells sit at the centre of this loop. The biochemistry review listed immune and inflammatory cells among the cells that both respond to and release substance P (PMID 32119470). A 2025 study in Cell reported that a mast cell receptor mediated post-stroke brain inflammation via a dural-brain axis, identifying meningeal mast cells as a relay between peripheral neuropeptide signalling and parenchymal brain inflammation (PMID 40712576). That work was preclinical, and the authors described a mechanism rather than a treatment (PMID 40712576).

Step 5: Pain signalling

In pain neurobiology, substance P is described as a co-transmitter released from C-fibre terminals in the dorsal horn, where NK-1 receptor activation on second-order neurons contributes to the slow, summating component of nociceptive transmission. A review of substance P and pain chronicity examined the peptide's role in the transition from acute to persistent pain and in central sensitisation (PMID 30284083). A 2025 narrative review of neuromodulatory signalling in chronic pain patients likewise placed substance P among the neuropeptide systems implicated in chronic pain states (PMID 40940732).

An important nuance in this literature: a mechanism being present in animals has not translated into a successful analgesic drug class. The substance P and pain chronicity review discussed the gap between strong preclinical rationale for NK-1 receptor involvement and the clinical record of NK-1 antagonism in pain (PMID 30284083).

Step 6: Itch

Itch and pain share sensory machinery, and substance P is discussed as a pruritogenic mediator acting both directly on neurons and indirectly through mast cells. A review of NK-1 receptor antagonists in pruritus summarised the clinical development of this drug class across different itch aetiologies (PMID 33675531). A separate commentary on the challenge of basic itch research set out why mechanisms demonstrated in rodent models have translated unevenly to human pruritus (PMID 31940043).

Step 7: Central nervous system roles

Substance P and NK-1 receptors are expressed in brain regions associated with stress, affect and seizure networks. A review of substance P regulation in epilepsy examined how the peptide and its receptor are altered in seizure models and what that implies for excitability (PMID 28474564). The review treated this as a regulatory system under investigation rather than a settled therapeutic target (PMID 28474564).

Proposed mechanisms still under investigation

Several lines of work propose that substance P-NK-1 signalling influences cell proliferation and survival in tumour biology. A review of neuroendocrine factors in melanoma pathogenesis discussed peptidergic signalling, including tachykinins, among the neuroendocrine inputs implicated in melanoma biology (PMID 34068618). A 2025 review of peptidergic systems and neuroblastoma similarly reviewed substance P and related peptides in that tumour context (PMID 40331938). Both were reviews of largely preclinical literature and did not establish clinical outcomes (PMID 40331938).

Established versus proposed: a summary

Context-dependent effects: What Studies Report

A recurring theme in the cited literature is that the same receptor system produced opposite-looking outputs depending on tissue and timing. Researchers reported that substance P attenuated colitis in a preclinical model by suppressing inflammation and ferroptosis through cGAS-STING (PMID 38725846), while other work reported that neuropeptide-driven sensory-immune crosstalk amplified inflammation, as in the urethral tuft-cell model of neurogenic inflammation (PMID 41032411) and the post-stroke mast cell dural-brain axis (PMID 40712576). Because the system is so widely distributed, the pruritus review emphasised that blocking NK-1 receptors is a systemic intervention with effects beyond the target tissue, and summarised the tolerability profile recorded during clinical development of these agents (PMID 33675531). None of the cited papers reported safety data for substance P administered to healthy people.

Limitations of the mechanism evidence

• Species gap. The 2025 mast cell, tuft cell and TRPV1 findings were animal studies, and the authors described them as mechanistic models (PMID 40712576, PMID 41032411, PMID 40489620).
• Translation record. The pain chronicity review discussed the mismatch between preclinical NK-1 rationale and clinical analgesic results (PMID 30284083).
• Model limitations in itch. A commentary set out why basic itch research has been difficult to translate to human pruritus (PMID 31940043).
• Reviews, not trials. The melanoma and neuroblastoma papers were narrative reviews of peptidergic signalling, not outcome studies (PMID 34068618, PMID 40331938).

Related reading

For background on what substance P is, where it is found and how the research literature is organised, see the overview page at /learn/substance-p/.

References

• Biochemistry, Substance P (StatPearls, 2023)
• A mast cell receptor mediates post-stroke brain inflammation via a dural-brain axis (Cell, 2025)
• Neuropeptide substance P attenuates colitis by suppressing inflammation and ferroptosis via the cGAS-STING signaling pathway (International Journal of Biological Sciences, 2024)
• Sleep deficiency exacerbates periodontal inflammation via trigeminal TRPV1 neurons (PNAS, 2025)
• Neuromodulatory Signaling in Chronic Pain Patients: A Narrative Review (Cells, 2025)
• Substance P and pain chronicity (Cell and Tissue Research, 2019)
• Substance P Regulation in Epilepsy (Current Neuropharmacology, 2018)
• Neuroendocrine Factors in Melanoma Pathogenesis (Cancers, 2021)
• Peptidergic Systems and Neuroblastoma (International Journal of Molecular Sciences, 2025)
• Tuft cells trigger neurogenic inflammation in the urethra (Cell Reports, 2025)
• The Challenge of Basic Itch Research (Acta Dermato-Venereologica, 2020)
• Neurokinin 1 Receptor Antagonists for Pruritus (Drugs, 2021)