Nociceptin
Also known as: Orphanin FQ, N/OFQ, nociceptin/orphanin FQ, NOP receptor ligand, ORL1 ligand
Endogenous opioid-related peptide; NOP receptor (ORL1/OP4) agonist — 17-amino-acid heptadecapeptide
What it is
Nociceptin (also called orphanin FQ) is a natural pain-regulating peptide made in your brain that helps control how you feel pain, anxiety, and stress. Researchers are studying it and drugs that mimic it as potential treatments for chronic pain, depression, migraine, and substance use disorders — without the addiction risk of traditional opioids.
The scientific side
nociceptin (N/OFQ) is a 17-amino-acid endogenous peptide that acts as the selective endogenous ligand of the NOP receptor (also designated ORL1 or OP4), a Gi/o-protein-coupled receptor. Despite being structurally homologous to dynorphin A, N/OFQ does not bind classical opioid receptors (mu, delta, or kappa), and its receptor is insensitive to naloxone — a key pharmacological distinction from the traditional opioid peptide system. Upon NOP receptor binding, N/OFQ activates inhibitory Gi/o signaling, leading to decreased cyclic AMP production, inhibition of voltage-gated calcium channels (including Cav1.2 L-type channels), and activation of inwardly rectifying potassium channels. This combination of ion channel effects reduces neuronal excitability and dampens neurotransmitter release at both central and peripheral synapses. At the spinal level, intrathecal N/OFQ produces antinociception by inhibiting afferent pain fiber signaling, while supraspinal (intracerebroventricular) administration paradoxically produces pronociceptive or hyperalgesic effects — a bidirectional modulation that reflects the region-specific distribution and function of NOP receptors across the neuraxis. The NOP receptor system also plays a significant role in stress-pain interactions: NOP receptors are upregulated by chronic stress, and the N/OFQ system modulates both stress-induced analgesia and stress-induced hyperalgesia. Preclinical and translational studies demonstrate NOP receptor expression in human sensory neurons and trigeminal ganglia, where NOP agonism produces greater inhibition of capsaicin responses than mu-opioid receptor activation, supporting peripheral analgesic potential. Beyond pain, NOP receptor signaling is implicated in anxiety regulation through prefrontal-amygdala circuits, urinary bladder control, reward and feeding behavior, and migraine pathophysiology via interaction with calcitonin gene-related peptide (CGRP) in trigeminal pathways. The mixed NOP/mu-opioid partial agonist cebranopadol demonstrates that co-activation of NOP and mu receptors can provide potent analgesia while substantially reducing the respiratory depression and addiction liability associated with selective mu-opioid agonists, validating the NOP system as a clinically actionable analgesic target. (PMIDs: 10998527, 26878436, 17532097, 27127846, 42218133, 42242546, 37209211, 32948048, 30430260)
Class: Endogenous opioid-related peptide; NOP receptor (ORL1/OP4) agonist — 17-amino-acid heptadecapeptide
Administration & storage
- Administration
- Intrathecal (i.t.) injection — spinal antinociceptive studies in preclinical modelsIntracerebroventricular (i.c.v.) injection — supraspinal pronociceptive/hyperphagic studies in preclinical modelsIntravenous (i.v.) infusion — cardiovascular and systemic pharmacokinetic studies in preclinical modelsIntravesical instillation — early clinical overactive bladder studiesSubcutaneous or intraperitoneal injection — used with some non-peptide NOP ligands and NOP antagonists in preclinical models
- Storage
- Synthetic N/OFQ peptide: store lyophilized at -20°C. Reconstituted solution: use fresh or store at -80°C and avoid repeated freeze-thaw cycles. Peptide is susceptible to protease degradation in plasma (in vitro half-life 2–3 hours). UFP-112 has approximately 2.6–3.5-fold longer plasma/brain half-life than native N/OFQ.
- Cautions
- Cardiovascular depression: Systemic NOP receptor activation causes significant decreases in heart rate and blood pressure. Intravenous UFP-112 produced marked sustained cardiovascular depression in rats at 0.1–10 nmol/kg. Any systemic administration in humans would require cardiovascular monitoring.,Bidirectional pain modulation — route-dependent: Supraspinal N/OFQ administration is pronociceptive (hyperalgesic) while spinal administration is antinociceptive. This means systemic dosing could have unpredictable pain effects depending on which receptor compartment is predominantly engaged.,Locomotor suppression: Supraspinal NOP agonism causes dose-dependent inhibition of spontaneous locomotor activity, lasting >6 hours at high analogue doses in rodents. This CNS depressant effect would be a safety concern for systemic human dosing.,No human safety database for N/OFQ peptide itself: There are no published Phase I trials of exogenous N/OFQ peptide administration in humans as of 2026. Safety data are entirely from preclinical studies and from clinical trials of small-molecule NOP ligands. Extrapolation to human peptide dosing is not supported.,Nausea/vomiting potential: Endogenous opioid system activation can cause nausea and vomiting. Mixed NOP/MOP agonists in clinical trials showed improved tolerability vs. classical opioids, but NOP peptide-specific emetic liability in humans is not established.
Legal & regulatory status
Nociceptin itself is not FDA-approved as a therapeutic agent. No NOP-selective peptide agonist has received FDA approval as of 2026. Cebranopadol, a mixed NOP/mu-opioid receptor partial agonist that acts on the same…
Nociceptin as an endogenous peptide does not appear on the WADA Prohibited List as a distinct entry. However, synthetic NOP receptor agonists and mixed NOP/opioid receptor agonists (such as cebranopadol) may fall under…
Nociceptin is not approved by Health Canada as a therapeutic drug. No NOP-selective agonist peptide has received Health Canada marketing authorization as of 2026. Research on the NOP receptor system and cebranopadol…
What it's studied for
- Chronic and neuropathic pain — NOP receptor agonism as analgesic strategy Preclinical + Phase II/III (via cebranopadol)
- Anxiety and stress disorders — NOP receptor antagonism as anxiolytic approach Preclinical + Phase I/II human imaging
- Migraine prevention and treatment — NOP agonism targeting trigeminal pain pathways Preclinical + Pilot Clinical (CGRP interaction)
- Overactive bladder and urinary incontinence — intravesical NOP agonism Preclinical + Early Clinical
- Depression and anhedonia — NOP antagonism as antidepressant strategy Preclinical + Phase I/II
- Inflammatory bowel disease — NOP/cannabinoid receptor crosstalk in gut inflammation Preclinical
- Substance use disorders — NOP agonism to reduce drug reward and relapse Preclinical
Safety signals
- Cardiovascular depression — heart rate and blood pressure reduction
- Route-dependent bidirectional pain modulation — pronociception risk with central delivery
- Central nervous system depression — locomotor suppression and sedation
- Hyperphagia and increased food intake — NOP agonism stimulates feeding
- Stress-pain interaction dysregulation — NOP system upregulation by chronic stress
- Unknown safety profile for exogenous peptide administration in humans
- Potential immunomodulatory effects — NOP system in inflammatory and immune-mediated disease
Contraindications
About these dose ranges
Dose ranges below reflect commonly reported community protocols. Where published research cites a specific dose, the PMID is linked. Doses without citations are not clinical recommendations — they reflect what practitioners and researchers commonly report using.
Community-reported dosing
| Route | Dose | Frequency / Duration | Population / context | Source tier |
|---|---|---|---|---|
| Unspecified | 1–100 pmol (N/OFQ); UFP-112 approximately 100-fold more potent than N/OFQ | — | Preclinical rodent models — intracerebroventricular (supraspinal) | Research |
| Unspecified | 1–100 pmol (N/OFQ and analogues) | — | Preclinical rodent models — intrathecal (spinal) | Research |
| Unspecified | Not specified precisely in available abstracts; intravesical instillation | — | Overactive bladder patients — intravesical clinical study | Research |
| Unspecified | 0.1–10 nmol/kg intravenous | — | Preclinical cardiovascular (rat, intravenous) — NOP agonist UFP-112 | Research |
| Intracerebroventricular, intrathecal, intravenous, or intravesical depending on study design | N/OFQ peptide: 1–100 pmol i.c.v. or i.t. in rodents; synthetic analogues (UFP-112) approximately 100-fold more potent | Single or repeated doses per experimental protocol | Preclinical rodent and non-human primate research models; early-phase clinical research with NOP-targeted small molecules |