Substance P

An endogenous 11-amino-acid tachykinin encoded by the TAC1 gene that activates the neurokinin-1 receptor in pain, vasodilation and neuroimmune signaling, with no approved product anywhere and only small human provocation studies.

Also referenced as: SP, SP(1-11), Substance P acetate

Also appears in: Immune

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What is Substance P?

Substance P is a native human neuropeptide: an undecapeptide with the sequence Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-Met and a C-terminal amide, formula C63H98N18O13S and a molecular weight of 1,347.6 (CAS 33507-63-0). It is the founding member of the tachykinin family, named for the shared C-terminal Phe-X-Gly-Leu-Met-NH2 motif that defines the group, and it is the preferred endogenous agonist at the neurokinin-1 (NK1) receptor.

The name dates to 1931, when von Euler and Gaddum described an unidentified depressor substance in horse brain and intestine extracts that lowered blood pressure and contracted isolated gut; the dried powder preparation gave the compound its letter (von Euler and Gaddum, Journal of Physiology, 1931;72(1):74-87). Forty years passed before the active principle was purified from bovine hypothalamus and sequenced (Chang et al., Nature: New Biology, 1971;232(29):86-87), with a chemical synthesis confirming the structure in the same issue (Tregear et al., Nature: New Biology, 1971;232(29):87-89). The peptide is encoded by the TAC1 gene, originally characterized as preprotachykinin A, whose transcripts are processed by tissue-specific alternative splicing into precursors yielding substance P alone or substance P with neurokinin A (Nawa et al., Nature, 1984;312(5996):729-734).

In the body, substance P is concentrated in small-diameter, capsaicin-sensitive sensory neurons and in enteric and autonomic nerves, and is released from their terminals in the spinal dorsal horn and in peripheral tissue during noxious stimulation and injury. Its pharmacology sits at the junction of pain transmission, vasodilation, plasma extravasation and immune-cell recruitment, which is why it is also a reference agonist in immunology and dermatology work (Mashaghi et al., Cellular and Molecular Life Sciences, 2016;73(22):4249-4264). No substance P product has ever been approved as a medicine in any jurisdiction, and the molecule circulates almost entirely as a laboratory reagent, typically as the acetate salt, alongside sensory neuropeptides such as CGRP and VIP.

How it works

• Agonist at the NK1 receptor. The rat substance P receptor was cloned and expressed in 1990, establishing NK1 as a G protein-coupled receptor rather than an enzyme target (Hershey and Krause, Science, 1990;247(4945):958-962). Cryo-electron microscopy structures of substance P-bound human NK1 in complex with Gq and with Gs show the peptide inserting its amidated C-terminus deep into the orthosteric pocket while a polar network at the solvent-exposed receptor surface shapes the entrance, and they explain both the receptor’s lack of basal signaling and the long-lasting, insurmountable conformation that antagonists impose (Thom et al., Science Advances, 2021;7(50):eabk2872).
• Dual Gq and Gs coupling set by superficial contacts. Substance P drives both Gq and Gs signaling at NK1, while the truncated fragment SP6-11 drives Gq alone. Structures and molecular dynamics attribute the difference to contacts between the peptide’s N-terminal half and the receptor’s extracellular loops: those contacts restrict the ligand’s flexibility and are required for potent Gs signaling but not for Gq signaling, so agonist dynamics rather than pocket occupancy set the signaling profile (Harris et al., Nature Chemical Biology, 2022;18(1):109-115).
• A second, non-NK1 route through mast cells. Substance P is also an agonist at the mast-cell receptor MRGPRX2 and its mouse homolog Mrgprb2. In mice, Mrgprb2 mediates inflammatory mechanical and thermal hyperalgesia and the recruitment of innate immune cells to an injury site, and substance P triggers cytokine and chemokine release from human mast cells through MRGPRX2 independently of NK1 (Green et al., Neuron, 2019;101(3):412-420.e3). The flare-and-wheal response to intradermal substance P therefore has a mast-cell component that NK1 blockade does not fully cover.
• Rapid peptidase clearance. In rat and human plasma, most substance P hydrolysis is carried out by dipeptidyl peptidase IV, which trims the peptide sequentially to SP(3-11) and SP(5-11), after which aminopeptidase M degrades the fragment several times faster still; angiotensin-converting enzyme contributes comparatively little (Wang et al., Peptides, 1991;12(6):1357-1364). Systemic exposure after injection is correspondingly brief, which is one reason intact substance P has not been developed as a systemic therapy.

Research status

Human vascular and sensory pharmacology. The best-characterized human work uses substance P as a probe rather than a treatment. In 16 healthy male volunteers, intra-arterial substance P increased forearm blood flow, and the response was abolished by the selective NK1 antagonist L-754,030 given as its intravenous prodrug L-758,298, while the antagonist did not alter basal vascular tone, showing that NK1 mediates substance P vasodilation but not resting vascular tone (Newby et al., British Journal of Clinical Pharmacology, 1999;48(3):336-344).

Headache provocation. The Danish Headache Center ran a double-blind, placebo-controlled, two-way crossover study in which 21 healthy adults received a 20-minute intravenous infusion of substance P or isotonic saline (NCT06632080). Headache within 12 hours was reported by 15 of 21 participants (71%) after substance P against 2 of 21 (10%) after placebo (p less than 0.001), the area under the curve for headache intensity was higher after substance P (p = 0.03), and superficial temporal artery diameter increased significantly (p = 0.005) (Al-Khazali et al., Cephalalgia, 2025;45(5):3331024251336132). A follow-on crossover study in people with migraine without aura (NCT06959004, 21 participants estimated) began on May 13, 2025 and lists primary completion for May 1, 2026; as of November 2026 no results have been posted to the registry.

Use as a challenge agent. GlaxoSmithKline ran an open-label study in 32 healthy participants to establish the optimum method for using intradermal substance P as a challenge agent against saline and histamine comparators, completed on July 21, 2021 with results posted (NCT04676763). Earlier, a four-way crossover phase 1 study used intradermal substance P as the itch stimulus to test the NK1 antagonist VLY-686, later named tradipitant, in 12 healthy volunteers (NCT01919944). In both designs substance P is the provocation, not the candidate drug.

Allergy, an unreplicated early finding. An uncontrolled study at Northwestern gave substance P together with a single allergen, by aerosol and then by injection, to subjects reactive to more than one allergen, using the second allergen as a within-subject control; IgE-mediated reactivity fell to both the administered and the control allergen in 7 of 8 subjects, two subjects reported a sustained reduction in ragweed symptoms, and no significant reactions to the injections occurred, with the authors calling for controlled work (Patterson et al., Journal of Laboratory and Clinical Medicine, 1999;133(2):189-199). A phase 1 follow-up of substance P injections in seasonal allergic rhinitis enrolled 40 participants and completed on June 20, 2017 (NCT01280149); no results have been posted and no publication followed.

Type 1 diabetes, preclinical promise and a stalled trial. In diabetes-prone NOD mice, eliminating TRPV1-positive pancreatic sensory neurons prevented insulitis and diabetes despite persistent autoreactive T cells, and intra-arterial substance P injected into the NOD pancreas reversed insulin resistance, insulitis and diabetes for weeks (Razavi et al., Cell, 2006;127(6):1123-1135). The one registered attempt to translate this, a phase 1 study of substance P in recent-onset type 1 diabetes sponsored by Vanilloid Genetics with an estimated 12 participants, started in May 2016 and has carried an unknown registry status since its May 2020 update, with no results and no publication.

Regeneration and wound healing. Substance P was identified as an injury-inducible systemic messenger that mobilizes CD29-positive stromal-like cells; intravenous injection mobilized such cells in uninjured mice, rats and rabbits, and both injection and transfusion of autologous mobilized cells accelerated healing in a rabbit alkali burn model (Hong et al., Nature Medicine, 2009;15(4):425-435). Follow-up work delivered substance P on self-assembling peptide nanofibers in a rat osteoarthritis model (Kim et al., Biomaterials, 2016;74:119-130). None of this line has reached a registered human trial.

Fragment-based ophthalmic use. The one clinical application derived from this peptide uses a fragment. Eye drops combining the substance P C-terminal tetrapeptide FGLM-NH2 with the insulin-like growth factor 1 fragment SSSR healed persistent epithelial defects in neurotrophic keratopathy in case reports and a small series (Chikama et al., Lancet, 1998;351(9118):1783-1784; Nishida et al., Japanese Journal of Ophthalmology, 2007;51(6):442-447), and the effect was later shown to depend on NK1 (Yanai et al., Investigative Ophthalmology and Visual Science, 2020;61(8):29). No such product has been approved.

The approved pharmacology runs the other way. Every marketed drug in this pathway blocks the receptor. Drugs@FDA records aprepitant (Emend, NDA 021549) as approved on March 26, 2003, with intravenous and generic forms following, and tradipitant (Nereus, NDA 220152) as approved on December 30, 2025. Both are small-molecule NK1 antagonists. As of November 2026 Drugs@FDA lists no application for substance P, DailyMed holds no labeling for it, and no sponsor has an active US development program for the peptide.

Common dosage forms

• Laboratory-reagent powder. Lyophilized substance P acetate in milligram-scale vials, labeled for laboratory use only, is the only widely available presentation.
• Study-prepared sterile solution for infusion. The Copenhagen provocation studies used a sterile substance P solution for intravenous infusion prepared for those protocols alone.
• Intradermal challenge solution. Clinical pharmacology units have prepared substance P as a sterile intradermal challenge solution given by trained investigators.
• No approved presentation. No approved vial, ampoule, pen, tablet or nasal presentation of substance P exists in the US or elsewhere, and the FDA recognizes no compounded dosage form.

Key considerations

• Regulatory status. The Research Market status reflects the absence of any FDA-approved substance P product and of any registered US development program aimed at approval. Substance P is not approved as a medicine in other jurisdictions either, and the only registered interventional study of substance P as a therapy has carried an unknown registry status since 2020.
• Human exposure is small and investigational. Published human experience amounts to a few dozen participants across vascular probes, headache provocation, intradermal challenge and one uncontrolled allergy series. Plasma peptidases degrade the molecule within minutes, and no trial has tested repeated systemic exposure for a therapeutic endpoint.
• Provoking symptoms is the reproducible human effect. The controlled human result is that intravenous substance P induces headache and arterial dilation in most healthy recipients, and intradermal injection produces flare, wheal and itch reliably enough to serve as a standardized challenge. Anything described as a benefit of administering the peptide to people rests on animal models or uncontrolled series.
• NK1 antagonists are not the same thing. Aprepitant and tradipitant block the receptor that substance P activates. They are distinct small molecules with opposite pharmacology, not alternative names for this peptide, and their approvals say nothing about the safety or efficacy of administering substance P.
• Naming. Substance P, SP and SP(1-11) all denote the same undecapeptide, usually supplied as the acetate salt; the fragments SP6-11 and FGLM-NH2 are distinct, shorter molecules with different signaling behavior. Listings under a generic “tachykinin” heading may instead be neurokinin A or neurokinin B, which share the C-terminal motif but have different receptor preferences.