Orexin B
hypocretin-2, HCRT-2, prepro-orexin residues 70-97
Orexin B, also called hypocretin-2, is the second peptide cleaved from the prepro-orexin precursor. It is a linear 28-residue amidated peptide that binds OX2R with high affinity and OX1R roughly ten to twenty times more weakly. It is a legitimate research neuropeptide with no cosmetic or dermatological application whatsoever, and it has never been administered to humans in a published trial.
Mechanism
Orexin B is cleaved from the same 130-residue prepro-orexin precursor as orexin A, from residues 70 to 97, and is C-terminally amidated. Structurally it is much simpler than its partner: a linear peptide with no disulfide bonds and no N-terminal pyroglutamate, which makes it correspondingly less stable in circulation. In solution it adopts two alpha-helices connected by a short linker, and both the amidated C-terminus and the C-terminal helix are essential for receptor activation. The C-terminal region carries the message, while the N-terminal region contributes to affinity and receptor discrimination.
Its receptor pharmacology defines its role. OX2R binds orexin A and orexin B with comparable affinity; OX1R binds orexin A roughly an order of magnitude more tightly than orexin B (reported IC50 values of the order of 20 nM versus several hundred nM). Orexin B is therefore best described as OX2R-preferring rather than OX2R-selective. Both receptors couple principally to Gq, activating phospholipase C, mobilising intracellular calcium and producing neuronal excitation. Because OX2R signalling in the histaminergic tuberomammillary nucleus is the dominant pathway for sustaining wakefulness, orexin B's receptor preference maps onto the arousal-maintaining arm of the system rather than the REM-regulating and reward-associated arm attributed more to OX1R.
Structural biology on this system is real but narrower than often stated. Yin and colleagues (2016) determined crystal structures of the human OX1R bound to antagonists and used molecular modelling, not crystallography, to explain subtype selectivity at OX2R. Those structures revealed a conserved amphipathic helix in the receptor's extracellular N-terminal region that interacts with orexin-A and is essential for high-potency neuropeptide activation at both receptors. This work underpins the entire orexin drug class, none of which uses the peptide itself.
What the research shows
Orexin B was identified alongside orexin A by Sakurai and colleagues in 1998 and, in parallel as hypocretin-2, by de Lecea and colleagues. The subsequent two decades established the receptor pharmacology, the anatomy of the orexin projection system, and the causal link between orexin loss and narcolepsy type 1. Yin and colleagues (2016) crystallised the human OX1R with the selective antagonist SB-674042 and with suvorexant, and modelled OX2R selectivity from those structures.
Orexin B itself has never been given to a human being in a published study. This is not an oversight. A linear, unmodified 28-residue peptide is degraded quickly in plasma, and (unlike orexin A, which crosses the blood-brain barrier by simple diffusion, albeit modestly) orexin B does not achieve meaningful central penetration after peripheral administration. Even the small intranasal human pilot work in narcolepsy used orexin A.
One animal study deserves careful reading because it is routinely misdescribed. Yamamoto and colleagues (2022) tested whether OX2R activation alone is sufficient to rescue narcolepsy phenotypes in orexin knockout mice. The agonist they used was [Ala11, D-Leu15]-orexin-B (a peptidic, modified analogue of orexin B, not a small molecule), and it was given by intracerebroventricular injection, that is, directly into the brain, bypassing the blood-brain barrier entirely. It extended wake time, reduced wake-to-NREM transition frequency and reduced cataplexy-like episodes to the same degree as orexin-A, and unlike orexin-A it did not induce drug-seeking behaviour in wild-type mice. This is a genuinely important result for the target, and it is also a precise demonstration of the problem: the orexin-B-derived pharmacology works when the peptide is injected into the brain. Nothing in it supports peripheral administration.
The clinically successful agents on the agonist side are small molecules. Danavorexton, an OX2R-selective small molecule, produced dose-dependent increases in Maintenance of Wakefulness Test sleep latency up to the 40-minute ceiling in narcolepsy type 1 patients in phase 1 studies. The practical position is therefore stark. Orexin B is a well-characterised research tool with a clear receptor profile and a substantial supporting structural literature, and simultaneously a compound with zero human administration data. Anything sold as orexin B for human use rests on no evidence at all, and it has no connection to skin, ageing or cosmetics in any published work.
Evidence assessment
Preclinical only
There is no published human trial of administered orexin B of any kind; all data are receptor pharmacology, structural biology and animal work, and its negligible blood-brain barrier penetration makes systemic human administration pharmacologically unpromising.
Tiers are applied consistently across the library and re-checked when new trials read out. Read the grading method.
Key studies
Orexins and orexin receptors: a family of hypothalamic neuropeptides and G protein-coupled receptors that regulate feeding behavior Preclinical only
Identified orexin B as a 28-residue amidated peptide from the prepro-orexin precursor, and established that OX2R binds orexin A and orexin B with comparable affinity while OX1R binds orexin A roughly an order of magnitude more tightly.
The hypocretins: hypothalamus-specific peptides with neuroexcitatory activity Preclinical only
Independently identified the same peptides as hypocretin-1 and hypocretin-2 and demonstrated their neuroexcitatory action.
Structure and ligand-binding mechanism of the human OX1 and OX2 orexin receptors Preclinical only
Resolved the antagonist-bound hOX1R structure and revealed a conserved amphipathic helix in the extracellular N-terminal region that interacts with orexin-A and is essential for high-potency neuropeptide activation at both receptors.
OX2R-selective orexin agonism is sufficient to ameliorate cataplexy and sleep/wake fragmentation without inducing drug-seeking behavior in mouse model of narcolepsy Preclinical only
The OX2R-selective orexin-B analogue selectively activated OX2R-expressing histaminergic neurons, extended wake time, reduced wake-NREM transition frequency and reduced cataplexy-like episodes to the same degree as orexin-A, and unlike orexin-A did not induce dose-dependent drug-seeking behaviour in wild-type mice.
Orexin 2 receptor-selective agonist danavorexton improves narcolepsy phenotype in a mouse model and in human patients Mixed evidence
Danavorexton was well tolerated and associated with marked improvements in sleep latency in both narcolepsy types, with dose-dependent increases in Maintenance of Wakefulness Test sleep latency up to the 40-minute ceiling in narcolepsy type 1.
Safety
There is no human safety data for orexin B, because it has never been administered to humans in a published study. Inferences must be drawn from receptor pharmacology: OX2R agonism produces wakefulness, and orexin signalling has sympathoexcitatory and autonomic effects, so systemic agonism would not be a neutral intervention. Specific tolerability findings sometimes attributed to the danavorexton phase 1 programme could not be verified from the published abstract during this review and are not asserted here. In any case the more likely outcome of peripheral orexin B administration is rapid degradation and negligible central effect, which is its own kind of problem for anyone paying for it.
Material sold under 'for research use only' labelling carries no verification of identity, purity, correct C-terminal amidation or sterility. For orexin B, C-terminal amidation is required for receptor activation, so a preparation lacking it would be pharmacologically inert regardless of how much peptide it contained. Buyers should also be aware that supplier listings frequently confuse the human sequence (2899.3 Da) with the mouse sequence (about 2936 Da), which is a straightforward indicator of how carefully a given supplier characterises its material. That phrase on a vial is a legal device permitting the sale of unapproved compounds to consumers; it is not a quality standard and not a safety statement.
Regulatory status
| Jurisdiction | Status |
|---|---|
| United Kingdom | No MHRA marketing authorisation. Supply for human use would fall under the Human Medicines Regulations 2012 as an unlicensed medicinal product. Orexin receptor antagonists hold UK authorisations for insomnia; no orexin peptide does. |
| United States | Not FDA-approved for any indication. Sold only as a research reagent. No orexin peptide product has ever been approved; the approved drugs acting on this system are small-molecule orexin receptor antagonists for insomnia (suvorexant, lemborexant, daridorexant), and OX2R agonists remain investigational. Supply for human use would constitute distribution of an unapproved new drug. |
| WADA (sport) | Prohibited under S0 (Non-Approved Substances), covering at all times any pharmacological substance not addressed elsewhere on the List and with no current approval by any governmental regulatory health authority for human therapeutic use. |
Questions
Not in any published study we could locate. Even the small intranasal pilot work in narcolepsy used orexin A. Orexin B is a research reagent with a well-characterised receptor profile and no human administration data whatsoever.
Both come from the same precursor, but orexin A is 33 residues with an N-terminal pyroglutamate, a C-terminal amide and two internal disulfide bonds, while orexin B is a simpler linear 28-residue amidated peptide. Orexin A binds both receptors well; orexin B prefers OX2R by roughly ten to twentyfold over OX1R. Orexin A crosses the blood-brain barrier modestly by diffusion; orexin B essentially does not.
No. There is no dermatological, cosmetic or anti-ageing literature on orexin B at all. It is a hypothalamic arousal neuropeptide. Its presence in peptide retail catalogues reflects how those catalogues are assembled, not any biological connection to skin.
Almost certainly not, and that is the pharmacological point. The one study showing that an orexin-B-derived OX2R-selective agonist reverses narcolepsy phenotypes injected it directly into the brains of mice. Given peripherally, orexin B is degraded quickly in plasma and does not meaningfully cross the blood-brain barrier. That limitation is exactly why researchers developed small-molecule OX2R agonists instead.