Dynorphin

What is Dynorphin?

Dynorphin is the umbrella name for a family of endogenous opioid peptides derived from a single precursor protein, prodynorphin, encoded by the PDYN gene on human chromosome 20. The major bioactive products are dynorphin A in its 17-residue (Dyn A 1-17), 13-residue (Dyn A 1-13), and 8-residue (Dyn A 1-8) forms, dynorphin B (also called rimorphin), and alpha-neo-endorphin and beta-neo-endorphin. All carry the canonical Tyr-Gly-Gly-Phe-Leu opioid pharmacophore at the N-terminus, the same five-residue motif that opens the enkephalins, with C-terminal extensions that confer the defining property of the family: high selectivity for the kappa-opioid receptor (KOR) over the mu (MOR) and delta (DOR) receptors. Avram Goldstein and colleagues at Stanford isolated dynorphin from porcine pituitary in 1979 and named it from the Greek 'dynamis' (power) plus 'endorphin' after observing that Dyn A (1-13) was about 700 times more potent than Leu-enkephalin in the guinea-pig ileum bioassay. Three years later Charles Chavkin, Ian James, and Goldstein established in Science that dynorphin's pharmacological signature mapped specifically to the KOR, completing the triad of mu/beta-endorphin, delta/enkephalin, and kappa/dynorphin endogenous opioid systems. Functionally, the dynorphin/KOR system is the dysphoric and aversive arm of endogenous opioid signaling — it is induced by stress, drives negative affect, suppresses dopamine release in the nucleus accumbens, and produces psychotomimetic effects in humans, the opposite of beta-endorphin's euphoric and analgesic mu-receptor profile. Dynorphin itself is not a therapeutic. The translational story belonged to KOR antagonists, which block dynorphin signaling with the aim of relieving anhedonia and depression — but both lead compounds have now failed. Johnson & Johnson discontinued the Phase 3 VENTURA program for aticaprant (formerly JNJ-67953964) in adjunctive major depressive disorder in March 2025 for insufficient efficacy, and Neumora discontinued navacaprant in 2026 after its three Phase 3 KOASTAL trials all missed the primary endpoint. The drugs that actually reached approval at this receptor are kappa agonists used for itch, not antagonists used for mood.

What Dynorphin Is Investigated For

Dynorphin is an endogenous-biology and drug-target topic, not a peptide consumers take. Its scientific footprint covers four overlapping domains. First, stress and mood: Land, Bruchas, and Chavkin established in 2008 that stress activates the dynorphin/KOR system in the ventral striatum and that this activation is required for stress-induced dysphoria and aversion. Second, addiction: dynorphin signaling in the nucleus accumbens and ventral tegmental area is upregulated by chronic cocaine, opioid, and alcohol exposure, contributes to the negative-affect 'dark side' of addiction (the framework developed by George Koob and Nora Volkow), and drives stress-induced reinstatement of drug seeking. Third, psychotomimesis: kappa agonists including ketazocine and the natural product salvinorin A (the active principle of Salvia divinorum, identified as a non-nitrogenous KOR-selective agonist by Roth, Rothman, and colleagues in 2002) produce dysphoria, perceptual distortions, and dissociation in humans, an effect Pfeiffer mapped to KOR in 1986 and which is now understood as the mirror-image of how blocking KOR could relieve depression. Fourth, drug development: the FAST-MAS proof-of-mechanism trial led by Diego Pizzagalli and colleagues in 2020 demonstrated that selective KOR antagonism increased ventral-striatum activation to reward and improved anhedonia, validating the target. That proof-of-mechanism signal did not survive contact with Phase 3. Johnson & Johnson discontinued the VENTURA program for aticaprant in adjunctive major depressive disorder in March 2025, and Neumora discontinued navacaprant in 2026 after KOASTAL-1, -2 and -3 all missed the primary MADRS endpoint. The honest framing is that dynorphin biology has been mapped in extraordinary detail over four decades, that KOR antagonism was one of the most credible novel mechanisms in psychiatric drug development, and that it has now failed as a treatment for major depression — while KOR agonism has succeeded, in the far less glamorous indication of dialysis-associated itch. Aticaprant has not been abandoned outright: a Phase 1b trial began recruiting in March 2026 testing it as an adjunctive treatment in schizophrenia.

History & Discovery

Dynorphin was isolated and named by Avram Goldstein and colleagues at Stanford University in 1979. Goldstein, Tachibana, Lowney, Hunkapiller, and Hood reported in PNAS the purification from porcine pituitary of a 13-residue opioid peptide that was about 700 times more potent than Leu-enkephalin in the guinea-pig ileum longitudinal muscle preparation — the standard opioid bioassay of the era. The comparison is pointed, because dynorphin-(1-13) literally contains Leu-enkephalin at its own N-terminus: the paper's conclusion was that the C-terminal extension -Arg-Arg-Ile-Arg-Pro-Lys-Leu-Lys, rather than a new pharmacophore, was responsible for the hundredfold gain in potency. Goldstein coined the name 'dynorphin' from the Greek 'dynamis' meaning power, joined to 'endorphin,' to capture the unusual potency. Subsequent purification and sequencing established dynorphin A in its 17-residue parent form (Dyn A 1-17), with shorter 1-13 and 1-8 fragments generated by further proteolytic processing, plus a sister peptide dynorphin B (rimorphin) and the alpha-neo-endorphin and beta-neo-endorphin peptides — all sharing the canonical Tyr-Gly-Gly-Phe-Leu N-terminal opioid pharmacophore. Three years after the isolation paper, Charles Chavkin, Ian James, and Goldstein established the receptor identity in a 1982 Science paper, demonstrating that dynorphin's pharmacological signature matched the kappa-opioid receptor (KOR) defined by the prototype kappa agonist ethylketocyclazocine, with much lower potency at mu and delta receptors. This formally completed the assignment of endogenous opioid peptide families to receptor subtypes — beta-endorphin and enkephalins to mu and delta, dynorphins to kappa — and set up the modern framework of the endogenous opioid system. The molecular precursor was cloned the same year. Tatsuhiko Kakidani, Hiroaki Takahashi, and colleagues in Shosaku Numa's laboratory in Kyoto reported in Nature 1982 the cloning and sequencing of the porcine preprodynorphin (PDYN) cDNA, establishing the precursor structure that yields alpha-neo-endorphin, beta-neo-endorphin, dynorphin A, and dynorphin B through proprotein-convertase processing. PDYN joined POMC (the beta-endorphin precursor) and proenkephalin as the third member of the endogenous opioid precursor family. The functional story developed across two parallel lines. The clinical-pharmacology line, led by Pfeiffer, Brantl, Herz, and Emrich in a 1986 Science paper, established that the psychotomimetic, dysphoric, and perceptually disorienting subjective effects of kappa agonists in humans map specifically to KOR — separating them from mu-receptor euphoria and analgesia and providing the first formal link between KOR activation and aversive emotional states. The preclinical line, advanced by Charles Chavkin, William Carlezon, Andrew Holmes, Brendan Walker, Pietro Cottone, Toni Shippenberg, Michael Bruchas, and others over the following two decades, mapped the dynorphin/KOR system into the circuits of stress, addiction, and depression. Mague, Pliakas, Carlezon, and colleagues demonstrated in 2003 (JPET) that KOR antagonists are antidepressant-like in the forced-swim test. Land, Bruchas, and Chavkin established in 2008 (Journal of Neuroscience) that stress activates dynorphin/KOR signaling in the ventral striatum and that this activation is required for stress-induced dysphoria and place aversion. The Roth, Rothman, and colleagues 2002 PNAS paper identifying salvinorin A as a non-nitrogenous KOR-selective natural product agonist provided a structurally novel pharmacological tool and confirmed that the dissociative, dysphoric subjective effects of Salvia divinorum are mediated by the same receptor that endogenous dynorphin engages. Clinical translation accelerated in the 2010s. Selective small-molecule KOR antagonists with adequate pharmacokinetics for human use — JNJ-67953964 (aticaprant) from Johnson & Johnson and BTRX-335140 (navacaprant) from BlackThorn/Neumora — entered clinical development, and the 2020 FAST-MAS proof-of-mechanism trial led by John Krystal and Diego Pizzagalli demonstrated using reward-circuit fMRI and anhedonia ratings that selective KOR antagonism produced the predicted effects in patients. Aticaprant advanced through Phase 2 anhedonia trials into the Phase 3 VENTURA program for adjunctive major depressive disorder. Navacaprant completed a Phase 2 trial published in the Journal of Clinical Psychopharmacology in 2025 and entered the three-trial Phase 3 KOASTAL program. The clinical answer arrived faster, and more bluntly, than the field expected. In March 2025 Johnson & Johnson discontinued the VENTURA program for insufficient efficacy, stating that aticaprant was safe and well tolerated with no new safety signals; the registry records two of those trials as terminated for insufficient efficacy. Neumora's KOASTAL-1 had already missed its primary endpoint in January 2025, and the remaining KOASTAL trials followed — the registry entry for the last of them states that navacaprant “did not achieve the primary endpoint across three randomized controlled trials” and that the program was discontinued for lack of efficacy in MDD. As of late 2026 no kappa-opioid antagonist is approved for any indication, and the dynorphin/KOR field occupies the uncomfortable position of a target mapped in extraordinary mechanistic detail that has now failed twice in registrational trials for its flagship indication. The receptor's clinical validation came from the other direction entirely: peripherally restricted kappa agonists for pruritus, approved and in routine use.

How It Works

Dynorphin is a small protein your brain releases under stress. It sticks to a receptor called the kappa-opioid receptor, which is essentially the brain's 'feel bad' switch. When dynorphin activates this receptor, dopamine release in the brain's reward circuit drops, mood worsens, and a sense of aversion or dysphoria sets in. This is the opposite of beta-endorphin, the 'feel good' opioid peptide that activates the mu-opioid receptor and produces euphoria. The dynorphin system gets cranked up by chronic stress, by drug withdrawal, and in depression, which is why drugs that block the kappa-opioid receptor — aticaprant and navacaprant — were tested as a new kind of antidepressant. The idea was that turning down the brain's dysphoria signal would restore normal reward processing in people stuck in a depressed, anhedonic state. It was a good idea that did not survive large trials: both drugs failed in Phase 3 and were discontinued in 2025 and 2026. Drugs that activate the kappa receptor, kept out of the brain so they cannot cause dysphoria, did succeed — as treatments for the severe itch that affects dialysis patients.

Dynorphin peptides are derived from a single precursor protein, prodynorphin (preprodynorphin), encoded by the PDYN gene on human chromosome 20p13. Tatsuhiko Kakidani, Hiroaki Takahashi, and colleagues in Shosaku Numa's laboratory cloned and sequenced the porcine prodynorphin cDNA in 1982 (Nature), establishing the precursor structure that yields, through proprotein-convertase processing, the major bioactive products: alpha-neo-endorphin, beta-neo-endorphin, dynorphin A (1-17 with shorter 1-13 and 1-8 fragments generated by further cleavage), and dynorphin B (rimorphin, 1-13). All of these peptides begin with the canonical Tyr-Gly-Gly-Phe-Leu (YGGFL) opioid pharmacophore at the N-terminus, the same motif that opens Leu-enkephalin, with C-terminal extensions rich in basic residues that confer KOR selectivity. Dynorphin's defining pharmacology is selectivity for the kappa-opioid receptor (KOR, encoded by OPRK1) over the mu (MOR/OPRM1) and delta (DOR/OPRD1) receptors. The 1982 Chavkin, James, and Goldstein paper in Science formally established this assignment by showing that dynorphin's bioactivity profile in receptor-binding and bioassay studies matched the kappa pharmacology defined by the prototype kappa agonist ethylketocyclazocine. KOR is a G-protein-coupled receptor that signals predominantly through Gi/o, inhibiting adenylate cyclase, lowering cAMP, activating inwardly rectifying potassium channels, and inhibiting voltage-gated calcium channels — a hyperpolarizing, neurotransmitter-release-inhibiting profile. Critically, KOR also activates beta-arrestin-2 and downstream p38 MAPK signaling, a pathway that Bruchas and Chavkin and colleagues established as the molecular basis for the dysphoric and aversive subjective effects of KOR agonism. Anatomically, dynorphin is widely distributed in the central nervous system, with prominent expression in the striatum (dorsal and ventral, with dynorphin co-released with GABA from D1-receptor-expressing medium spiny neurons of the direct pathway), hypothalamus, hippocampal mossy fibers (where dynorphin is co-packaged in zinc-rich vesicles with glutamate), amygdala, periaqueductal gray, ventral tegmental area, locus coeruleus, and spinal cord dorsal horn. KOR has overlapping but distinct distribution, with high density in striatum, cortex, hypothalamus, claustrum, and dorsal raphe. Functionally, the dynorphin/KOR system is the dysphoric and aversive arm of endogenous opioid signaling. Acute and chronic stress activate prodynorphin transcription and dynorphin release in striatum, amygdala, and dorsal raphe (Land et al. 2008 Journal of Neuroscience), and KOR activation in the nucleus accumbens suppresses dopamine release, providing the cellular substrate for stress-induced anhedonia. Pfeiffer and colleagues established in 1986 that the psychotomimetic, dysphoric subjective effects of kappa agonists in humans map specifically to KOR rather than mu or delta. Mague, Pliakas, Carlezon, and colleagues showed in 2003 (Journal of Pharmacology and Experimental Therapeutics) that kappa antagonists are antidepressant in the rat forced-swim test, and the dynorphin/KOR system has subsequently been implicated in stress-induced reinstatement of drug seeking, the negative-affect dimension of addiction (Koob's 'dark side' framework, most recently reframed by Vendruscolo and Koob in Neuron 2026 around 'hyperkatifeia' and negative reinforcement in alcohol addiction), and the pathophysiology of major depression and anhedonia. The 2020 FAST-MAS proof-of-mechanism trial (Krystal, Pizzagalli, and colleagues, Nature Medicine and Neuropsychopharmacology) demonstrated that the selective KOR antagonist now known as aticaprant increased ventral-striatum activation to reward stimuli and improved anhedonia ratings in patients with mood and anxiety disorders, validating the receptor as a clinical antidepressant target. Three threads from the 2026 literature have deepened the mechanistic picture. Peng and colleagues (Translational Psychiatry 2026) showed that corticosterone-induced dynorphin A upregulation in the dentate gyrus overactivates KOR and suppresses Pax6, Neurog2, and NeuroD1 — obstructing adult hippocampal neurogenesis — and that nor-BNI rescues both the depressive-like behavior and the neurogenesis deficit, providing a cellular substrate for KOR-driven depression beyond the dopamine-suppression story. Han and colleagues (Nature Communications 2026) solved the cryo-EM structure of KOR bound to β-arrestin1 at 2.60 Å, identifying phosphorylation sites and a phospholipid-binding site that enhance arrestin recruitment — a structural anchor for the biased-agonism program that seeks to separate the Gi/o analgesic signal from the β-arrestin/p38 MAPK dysphoric signal. Jiang and colleagues (Nature Structural & Molecular Biology 2026) reported that ketamine and PCP directly bind and activate KOR, adding a nuance to the standard NMDA-antagonist framing of ketamine's antidepressant action. In the same period, Weiss and colleagues (Biological Psychiatry 2026) reported the first in-vivo [11C]EKAP PET evidence that KOR availability is reduced in the amygdala, anterior cingulate, hippocampus, insula, and frontal cortex of patients with borderline personality disorder, correlating with impulsivity and depressive symptoms — extending the KOR-availability abnormality beyond MDD into a second psychiatric diagnosis.

Evidence Snapshot

Research Gaps & Open Questions

What the current literature has not yet settled about Dynorphin:

• 01Why selective kappa-opioid receptor antagonism failed in Phase 3 despite a clean proof-of-mechanism signal — whether the FAST-MAS reward-circuit readout was a poor surrogate for clinical depression, whether the enrolled populations were insufficiently enriched for dynorphin-driven anhedonia, whether the doses achieved inadequate central receptor occupancy, or whether elevated kappa tone is a correlate rather than a cause of depression. The aticaprant and navacaprant failures make this the defining open question of the field.
• 02Whether KOR antagonism has any future outside major depressive disorder — in schizophrenia, where aticaprant entered Phase 1b adjunctive testing in 2026, or in substance use disorder or post-traumatic stress disorder — given that the MDD hypothesis has now failed in two independent Phase 3 programs.
• 03The role of biased KOR ligands — agonists that activate Gi/o without engaging beta-arrestin/p38 MAPK signaling — as potential analgesics without the dysphoric profile of conventional kappa agonists, an active medicinal-chemistry frontier newly enabled by the 2026 cryo-EM structure of the KOR–β-arrestin1 complex (Han et al., Nat Commun 2026), which resolves the phosphorylation sites and phospholipid-binding surface that drive arrestin recruitment.
• 04Whether long-term KOR antagonism affects stress responsivity, hypothalamic-pituitary-adrenal axis function, reward learning, or vulnerability to substance use over months and years of exposure — questions that Phase 3 and post-marketing data will need to address.
• 05The contribution of the dynorphin/KOR system to itch — the one place where kappa pharmacology has succeeded clinically, with difelikefalin approved for moderate-to-severe CKD-associated pruritus in hemodialysis patients and nalfurafine approved in Japan. The circuit basis is only now being resolved, and understanding why peripheral restriction preserves the antipruritic effect while discarding the dysphoria is the central design question for the next generation of kappa drugs.
• 06The non-opioid actions of dynorphin A on NMDA receptors, voltage-gated calcium channels, and bradykinin receptors at higher concentrations, and whether these contribute to spinal cord injury pathophysiology and chronic pain in clinically meaningful ways.
• 07Whether human PDYN gene polymorphisms or epigenetic regulation contribute to vulnerability to depression, addiction, and stress-related disorders, and whether genotype-stratified approaches could refine kappa-antagonist drug development.

Forms & Administration

Dynorphin is not formulated or approved as a therapeutic in any jurisdiction. Research applications use synthetic dynorphin A (1-17, 1-13, or 1-8) and dynorphin B for in vitro receptor binding and signaling assays, ex vivo tissue pharmacology, and intracerebroventricular or intrathecal administration in animal models. The clinically relevant products are on the agonist side, and they are deliberately kept out of the brain: difelikefalin (Korsuva in the US, Kapruvia in the EU) is a synthetic D-amino-acid tetrapeptide KOR agonist given as a 0.5 mcg/kg intravenous bolus into the venous line of the dialysis circuit at the end of each hemodialysis session, approved for moderate-to-severe CKD-associated pruritus; nalfurafine (Remitch) is an orally active KOR agonist approved in Japan for refractory pruritus in hemodialysis and chronic liver disease. Peripheral restriction is the design principle — it delivers the antipruritic effect while avoiding the central dysphoria that killed kappa agonists as analgesics. On the antagonist side, aticaprant (Johnson & Johnson, formerly JNJ-67953964) and navacaprant (Neumora, formerly BTRX-335140) were both oral brain-penetrant selective KOR antagonists; both programs were discontinued in major depressive disorder after Phase 3 failures, though aticaprant re-entered Phase 1b testing in schizophrenia in 2026. Earlier-generation tool antagonists (nor-binaltorphimine, JDTic) have long pharmacokinetics that limit clinical use and remain primarily research tools. Compounded dynorphin from peptide marketplaces has no validated clinical use, and consumers should be aware that dynorphin's pharmacology is dysphoric rather than rewarding.

Common Questions

Who Dynorphin Is NOT For

Drug & Supplement Interactions

There is no validated human drug-interaction profile for dynorphin because no dynorphin product has been clinically developed. Theoretical interactions follow from dynorphin's known signaling. At kappa-opioid receptors, exogenous dynorphin would oppose the mechanism of investigational KOR antagonists (aticaprant, navacaprant) being developed for depression. The dynorphin/KOR system suppresses dopamine release in the nucleus accumbens, which could in principle interact with dopaminergic medications used in Parkinson's disease (levodopa, dopamine agonists), antipsychotics (which block dopamine receptors), and stimulant medications used in ADHD. Because KOR activation lowers mood and produces dysphoria in humans, exogenous dynorphin could oppose the clinical effects of antidepressants (SSRIs, SNRIs, tricyclics, MAOIs) and could interact unpredictably with anxiolytics (benzodiazepines) and mood stabilizers. At higher concentrations, longer dynorphin A fragments interact with NMDA receptors independently of opioid receptors, with theoretical implications for interaction with NMDA antagonists (ketamine, memantine, dextromethorphan). Locally in the spinal cord, intrathecal dynorphin has been associated with motor deficits and excitotoxicity in animal models, an effect attributed to NMDA-receptor activity. None of these interactions has been characterized in controlled human studies; they are mechanistic possibilities that argue against casual exogenous dynorphin exposure rather than documented clinical events.

Safety Profile

Legal Status

Regulatory status changes over time. Verify current local rules with a qualified professional.

Myths & Misconceptions