Pain is not a single phenomenon. It is the end product of multiple distinct signaling pathways that sense tissue damage, transmit that signal to the central nervous system, amplify or dampen it at the spinal cord, and ultimately shape its conscious experience at supraspinal sites. Peptides are involved at every step. They serve as primary afferent neurotransmitters, mediators of neurogenic inflammation, modulators of dorsal-horn transmission, and messengers in the cranial vasculature where migraine originates. The last two decades have produced some of the most consequential drug approvals in pain medicine by systematically targeting these peptide pathways.
This guide profiles five peptides that have each reshaped a distinct corner of pain medicine or pain research. Substance P is the prototypical tachykinin, whose NK1 receptor ended up being the target of approved antiemetics rather than analgesics. Bradykinin sits at the center of the kinin-kallikrein cascade that produces vasodilation, plasma extravasation, and nociceptor sensitization. CGRP became the first broadly-validated neuropeptide drug target for migraine, with multiple FDA-approved monoclonal antibodies and gepants now in clinical use. Ziconotide — a marine cone-snail-derived peptide — is the only N-type calcium channel blocker approved for intrathecal use in refractory pain. Galanin is a multifunctional neuropeptide whose antinociceptive actions at the spinal cord have kept it in preclinical and translational pain research.
The focus throughout is on what each peptide does, what happened when pharmacology tried to target it, and which translational outcomes have held up in the clinic. Some of these stories — CGRP monoclonals for migraine — are among the clearest successes of neuropeptide drug development. Others, like substance P antagonists for pain, illustrate how strong a target can look preclinically and still fail in human pain trials. Both outcomes inform where future peptide analgesic development is most likely to succeed.
Peptides in Pain Pathways: Nociceptors to Supraspinal Modulation
Pain signaling begins at primary afferent nociceptors — specialized sensory neurons whose terminals in the skin, viscera, and deep tissues detect noxious mechanical, thermal, and chemical stimuli. These neurons are enriched in neuropeptides that serve as co-transmitters alongside glutamate. In the dorsal horn of the spinal cord, peptide release shapes synaptic gain, and descending modulation from supraspinal sites — the periaqueductal gray, rostral ventromedial medulla — further adjusts transmission based on attention, affect, and endogenous opioid tone.
Two broad classes of peptide action are relevant to analgesic drug development. Pro-nociceptive peptides — substance P, CGRP, and bradykinin among them — promote pain transmission and sensitization, either at the central synapse or by sensitizing peripheral nociceptors. Blocking these peptides or their receptors can, in principle, produce analgesia. Anti-nociceptive peptides — the endogenous opioids, nociceptin at spinal sites, and galanin at GalR1 — dampen transmission, and mimicking them can also produce analgesia.
This dual logic underlies the diversity of peptide-based pain pharmacology. Some approved drugs act as peptide-receptor antagonists (CGRP receptor antagonists for migraine), some deplete peptide release indirectly (ziconotide, blocking the calcium channels that drive pro-nociceptive peptide exocytosis), and some mimic endogenous analgesic peptides (the opioid class, covered in the companion endogenous-opioid-peptides guide). The five peptides profiled below span this range.
Substance P and the NK1 Receptor
Substance P is an 11-amino-acid member of the tachykinin peptide family with the sequence Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-Met-NH2. It is released from primary afferent nociceptors alongside glutamate and CGRP, and it acts primarily at the neurokinin-1 (NK1) receptor — a Gq-coupled GPCR — to promote neuronal excitation, synaptic facilitation, and neurogenic inflammation. Peripheral substance P release also triggers mast cell degranulation, vasodilation, and plasma extravasation, producing many of the hallmarks of inflammatory flare.
The substance P/NK1 axis looked, for most of the 1990s, like one of the most attractive pain drug targets ever characterized. Multiple pharmaceutical companies developed potent, orally-active NK1 receptor antagonists and moved them into large human pain trials. The results were one of the most-cited translational failures in neuropeptide drug development: NK1 antagonists consistently failed to produce clinically meaningful analgesia in humans despite strong preclinical activity in rodent pain models.
The NK1 antagonist class was eventually rescued by a different indication entirely. Aprepitant and related NK1 antagonists were found to potently prevent chemotherapy-induced nausea and vomiting, leading to FDA approval for that indication and establishing substance P/NK1 signaling as a validated target for emesis rather than pain. Substance P continues to appear in research on fibromyalgia, IBS, inflammatory arthritis, wound healing, and angiogenesis, but the story of NK1 as an analgesic target is, for now, a cautionary one about the limits of preclinical-to-clinical translation in pain.
Bradykinin and the B2 Receptor
Bradykinin is a nine-amino-acid peptide generated from kininogens by the enzyme kallikrein as part of the kinin-kallikrein cascade. It is one of the most potent endogenous vasodilators and a central mediator of pain and inflammation in injured tissue. Bradykinin acts through two G-protein-coupled receptors: B2, which is constitutively expressed and mediates most acute effects, and B1, which is induced in chronic inflammatory states.
B2 receptor activation stimulates phospholipase C, raises intracellular calcium, triggers nitric oxide synthase, and releases prostaglandins. The downstream effects — vasodilation, increased vascular permeability, smooth muscle contraction, and sensitization of nociceptors — make bradykinin a dominant pro-inflammatory and pro-nociceptive peptide at sites of tissue injury. The same cascade underlies clinically important phenomena including ACE-inhibitor-induced cough, because ACE inhibitors reduce bradykinin degradation and potentiate its tussigenic effects.
Clinically, the kinin axis is a validated drug target, though not quite in the direction expected from the peptide's role in pain. Icatibant (Firazyr), a selective B2 receptor antagonist, received FDA approval in 2011 for hereditary angioedema (HAE) — a condition driven by uncontrolled bradykinin production during C1-esterase inhibitor deficiency. Icatibant rapidly reverses HAE attacks by blocking B2-mediated vascular leak, establishing bradykinin antagonism as a legitimate pharmacological approach for edema. Dedicated bradykinin antagonists for chronic pain have not followed, however; pain indications have proven more difficult to translate than angioedema, likely reflecting the redundancy of pain pathways and the rapid degradation of endogenous bradykinin.
CGRP and the Migraine Revolution
Calcitonin gene-related peptide (CGRP) is a 37-amino-acid neuropeptide produced by alternative splicing of the calcitonin gene. It is one of the most potent endogenous vasodilators known and plays a central role in migraine pathophysiology, nociception, and cardiovascular regulation. In trigeminal afferents — the nerves that innervate the cranial vasculature — CGRP is released during migraine attacks, activating the trigeminovascular system and promoting neurogenic inflammation and peripheral sensitization.
The CGRP receptor — a complex of the calcitonin receptor-like receptor (CLR) and receptor activity-modifying protein 1 (RAMP1) — signals through Gs and cAMP elevation, producing potent vasodilation and modulating nociceptive transmission. The therapeutic implications took more than two decades to translate, but the payoff has been substantial. Plasma CGRP levels rise during spontaneous migraine attacks and normalize with triptan treatment, providing a biomarker that supported target validation long before drugs existed to test the hypothesis clinically.
As of 2026, multiple FDA-approved drugs target the CGRP pathway. Monoclonal antibodies — erenumab (against the CGRP receptor), fremanezumab and galcanezumab (against the CGRP ligand) — are approved for migraine prevention. Small-molecule CGRP receptor antagonists — the gepants, including rimegepant and ubrogepant — are approved for both acute treatment and prevention. The CGRP story is arguably the most successful neuropeptide drug-development program of the last two decades, validating the target concept and reshaping migraine medicine. Preclinical research continues to examine CGRP's roles in bone metabolism, wound healing, and cardiac function beyond its headache relevance.
Ziconotide: A Cone-Snail Peptide for Refractory Pain
Ziconotide is a synthetic 25-amino-acid peptide derived from omega-conotoxin MVIIA, a venom component of the predatory marine cone snail Conus magus. Unlike the other peptides in this guide, ziconotide is not an endogenous mammalian neuropeptide — it is a natural-product drug whose extraordinary channel selectivity made it a candidate for a very specific clinical niche. Ziconotide selectively and reversibly binds N-type voltage-sensitive calcium channels (Cav2.2) on the presynaptic terminals of primary afferent nociceptors in the dorsal horn. Blocking these channels prevents calcium-dependent exocytotic release of pro-nociceptive neurotransmitters including glutamate, substance P, and CGRP — effectively interrupting ascending pain signal transmission at the first central synapse.
Because of its peptide structure and selectivity profile, ziconotide cannot be administered orally or systemically. It is approved only for continuous intrathecal infusion via implanted drug-delivery pumps — a delivery mode reserved for severe chronic pain refractory to systemic analgesics and intrathecal morphine. FDA approval came in December 2004 under the brand name Prialt. The pivotal trial, published in JAMA in 2004, demonstrated a 31.2% reduction in visual analog scale pain scores versus 6.0% for placebo in patients with refractory malignant and non-malignant pain.
Ziconotide's positioning is a reminder that translation can succeed for narrow, well-matched indications even when systemic delivery fails. The drug is non-opioid, carries no addiction liability, and retains activity in opioid-tolerant patients — making it particularly valuable in that refractory population. The trade-offs are a narrow therapeutic index, significant CNS side effects that require careful dose titration, and the infrastructure burden of intrathecal pump management. Two decades after approval, it remains the only approved N-type calcium channel blocker in clinical use.
Galanin: An Antinociceptive Neuropeptide
Galanin is a 29-amino-acid neuropeptide (30 AA in humans) widely distributed in the central and peripheral nervous system and gastrointestinal tract. It is one of the most multifunctional neuropeptides known, modulating pain processing, cognition, mood, feeding, pancreatic insulin release, and cardiovascular function. For the purposes of pain research, the most relevant actions occur at the spinal dorsal horn and in the peripheral sensory system.
Galanin signals through three G-protein-coupled receptors: GalR1 and GalR3 couple to Gi/o and reduce neuronal firing, while GalR2 couples to Gq/11 and elevates intracellular calcium. In the dorsal horn, galanin is released from primary afferents alongside substance P and appears to serve as a counter-regulatory signal — inhibiting nociceptive transmission via GalR1 and blunting the excitatory co-transmitter cascade. The net pain phenotype of galanin is site-dependent: spinal effects are generally anti-nociceptive, while supraspinal galanin action can be pro-nociceptive in some models.
Galanin has not produced an approved pain drug, but it remains of interest for multiple reasons. Its cognitive implications in Alzheimer's disease — where galanin hyperinnervation of surviving cholinergic basal-forebrain neurons is proposed to inhibit acetylcholine release — drive selective GalR1/GalR3 antagonists and GalR2 agonists through preclinical development. Its pancreatic effects keep it relevant to diabetes research. Its pain role, while complex, illustrates a recurring theme: multifunctional neuropeptides with receptor subtypes that have opposing effects are pharmacologically interesting but hard to drug selectively in whole-animal or human settings.
Future Peptide Pain Therapeutics: What's Next
The five peptides in this guide, taken together, suggest a pattern for where peptide-pain drug development is most likely to succeed. Targets with clear biomarker validation and anatomically-restricted action — CGRP in cranial trigeminal afferents, N-type calcium channels at the first central synapse — have translated into approved therapies. Targets with strong preclinical signal but redundant biology and broad anatomical distribution — substance P/NK1 being the clearest example — have been harder to convert.
Several active research fronts extend these lessons. Mixed NOP/opioid agonists such as cebranopadol exploit a non-classical opioid pathway (covered in the endogenous opioid peptides guide) and have progressed into Phase II/III chronic pain trials. Peptide conjugates and delivery-modified formulations aim to extend the half-life of intrinsically short-lived peptides. Bispecific biologics targeting pairs of pain peptides — or pain peptide plus inflammatory cytokine — are an emerging class. Bradykinin-pathway biologics for hereditary angioedema continue to expand, offering a template for how to drug a pain-adjacent peptide cascade in a specific disease context.
For broader chronic pain — neuropathic pain, fibromyalgia, inflammatory pain syndromes where opioids carry addiction risk and NSAIDs carry GI and cardiovascular risk — the peptide field has not yet produced the breakthrough that migraine received with CGRP antagonism. The question is whether future successes will come from better targets, better delivery, better patient stratification, or all three. The peptides profiled in this guide are the foundational pharmacology that frames that question.
Frequently asked questions
Not for pain, despite decades of attempts. NK1 receptor antagonists like aprepitant consistently failed to produce clinically meaningful analgesia in human pain trials, even though preclinical rodent pain models suggested strong activity. The class was ultimately approved for chemotherapy-induced nausea and vomiting — validating the substance P/NK1 axis for emesis rather than pain. This is one of the most-cited translational failures in neuropeptide drug development.
Plasma CGRP levels were shown to rise during spontaneous migraine attacks and normalize with triptan treatment, providing biomarker-level target validation. The CGRP receptor — a complex of CLR and RAMP1 — signals in the trigeminovascular system that drives migraine pathophysiology. Multiple FDA-approved drugs now target this pathway: monoclonal antibodies (erenumab, fremanezumab, galcanezumab) for prevention and gepants (rimegepant, ubrogepant) for acute treatment and prevention.
Ziconotide is a 25-amino-acid peptide with three disulfide bridges — its size and structure prevent oral or systemic bioavailability and prevent crossing the blood-brain barrier from the periphery. Intrathecal delivery places the drug directly in the cerebrospinal fluid where it can act on N-type calcium channels at the spinal dorsal horn. The trade-off is that treatment requires an implanted drug-delivery pump, restricting use to severe chronic pain refractory to other therapies.
Galanin's pain effects are site-dependent. At the spinal cord, galanin is co-released with substance P from primary afferents and inhibits nociceptive transmission via the GalR1 receptor, serving as a counter-regulatory anti-nociceptive signal. Supraspinally, galanin action can be pro-nociceptive in some models. The mixed profile and redundant receptor subtypes have made it difficult to develop selective galanin-targeting analgesics despite sustained preclinical interest.
Yes, but for hereditary angioedema rather than pain. Icatibant (Firazyr), a B2 receptor antagonist, received FDA approval in 2011 for acute treatment of HAE attacks. Bradykinin is a central mediator of the HAE vascular-leak cascade, and B2 blockade rapidly reverses attacks. Dedicated bradykinin antagonists for chronic pain indications have not reached approval, likely reflecting redundancy in pain pathways and rapid endogenous bradykinin degradation.
Ziconotide is the most prominent approved peptide alternative for severe refractory pain — non-opioid, non-addictive, but intrathecal-only. CGRP-pathway drugs are peptide-biology-derived alternatives for migraine specifically. Mixed NOP/opioid agonists such as cebranopadol are in late-stage trials aiming to provide opioid-like analgesia with reduced reward signaling. For broader chronic pain, the peptide field has not yet produced the breadth of options available in migraine, and conventional opioids, NSAIDs, and gabapentinoids remain dominant despite their limitations.