D tier · weak
The biology is world-class but the peptide as an administered drug is not: exactly three published human studies exist, all intranasal, all from one German group, with 29 people in total ever exposed, and the one that measured wakefulness in narcolepsy found no significant increase in wakefulness. ClinicalTrials.gov holds zero registered studies in which orexin-A itself is the intervention.
orexin-a
Orexin A is an endogenous hypothalamic neuropeptide that, with orexin B, maintains arousal and stabilises the boundary between wake and REM sleep by activating the OX1 and OX2 receptors. Its deficiency is the established cause of narcolepsy type 1, which makes it one of the best-characterised neuropeptides in human medicine. Administering the peptide itself is a completely different proposition from understanding it, and the human administration literature amounts to three small intranasal crossover studies in narcolepsy.
// we supply this one
available as a research reagent
≥ 98% HPLC · lyophilised powder · batch certificate published. Grade D above is our own and is not adjusted because we stock it.
the explanation
Orexin A is a natural brain chemical that keeps you awake. People with narcolepsy have lost the cells that make it, which is why they fall asleep suddenly. Giving the chemical back as a nasal spray has only been tried in three tiny studies involving 29 people between them, and it did not actually make them more awake.
regulatory status
Not an approved medicine anywhere; research reagent only
Orexin A holds no marketing authorisation from the MHRA, EMA or FDA and is not a licensed medicinal product in the UK; material sold under this name is an unlicensed research chemical and lawful supply is for laboratory use, not human use. It is critical to be precise about what has been approved in this pathway: the licensed drugs are orexin receptor ANTAGONISTS, which do the opposite of the peptide — daridorexant, a dual orexin receptor antagonist, is licensed and NICE-recommended for long-term insomnia in adults in England (TA922, October 2023). Orexin A is not named anywhere on the WADA Prohibited List, but as a pharmacological substance with no current approval by any governmental regulatory health authority for human therapeutic use it falls within class S0 (Non-Approved Substances), prohibited at all times in and out of competition. It is not an authorised food supplement ingredient in the UK.
how it works · proposed mechanism
Orexin A and orexin B are both cleaved from a single precursor, prepro-orexin, made by a small population of neurons in the lateral and posterior hypothalamus. Orexin A is a full agonist at both orexin receptors, OX1R and OX2R, and is more potent than orexin B at OX1R. Its projections reach the monoaminergic and cholinergic arousal nuclei, so the peptide functions as a stabiliser of the waking state rather than a simple stimulant.
Loss of the neurons, not loss of the receptor
Post-mortem work found an 85–95% reduction in the number of orexin (hypocretin) neurons in narcoleptic brains compared with controls, with neighbouring melanin-concentrating hormone neurons preserved and gliosis present. That is why narcolepsy type 1 is framed as a deficiency state. The receptors themselves remain, which is the logic behind trying to replace the ligand.
Wake–REM boundary rather than raw wakefulness
In the intranasal narcolepsy studies the measurable effect was on sleep architecture, not on time awake. In the overnight polysomnography study, intranasal hypocretin-1 significantly reduced total REM sleep and markedly reduced direct wake-to-REM transitions, with a tendency to longer REM latency, but produced no statistically significant increase in wakefulness. The peptide behaved as a REM-stabiliser in that setting.
A delivery problem, not a receptor problem
Orexin A is a 33-residue, disulfide-bonded peptide, far too large for reliable passive brain entry by any convenient route, and the intranasal studies exist precisely because injecting it systemically is not a credible way to reach hypothalamic and brainstem targets. Nose-to-brain transfer in humans has never been quantified for this peptide, so every intranasal study is testing an unmeasured delivery assumption alongside the pharmacology.
The pathway's successes point away from the peptide
Two drug classes have validated orexin pharmacology in large trials and neither is the peptide. Receptor antagonists are approved for insomnia, and on the replacement side oveporexton (TAK-861), an oral small-molecule OX2R-selective agonist, met all primary and secondary endpoints in two phase 3 narcolepsy type 1 studies enrolling 168 and 105 participants. If orexin replacement becomes a real therapy it will almost certainly be a small molecule.
what’s reported
evidence shape
7 sourcesThe composition of the cited literature by study type. This describes the shape of the evidence, not its quality — and it does not by itself set the grade.
⚠ the catch
The famous facts about orexin A belong to orexin biology, not to orexin A as a product. Narcolepsy, the receptor antagonists, the phase 3 agonist programme — none of those involve giving anyone this peptide. Every human administration study is intranasal, unregistered, and from a single research group: 7 patients in a crossover for olfaction, 8 for overnight polysomnography and 14 for wakefulness and attention, 29 exposures in total, and because all three came from one group the participants may overlap. The overnight study reported no statistically significant increase in wakefulness, which is the specific claim most often attached to this compound, and nobody has ever measured how much intranasally applied orexin A actually reaches the human brain.
key published findings
- ClinicalTrials.gov contains zero registered studies in which orexin-A or hypocretin-1 is the administered intervention; every orexin entry in the registry is a receptor antagonist (suvorexant, lemborexant, daridorexant), an observational biomarker study, or the small-molecule agonist TAK-360.
- Post-mortem study of 4 narcoleptic and 12 control human brains found an 85–95% reduction in orexin neuron number, establishing narcolepsy type 1 as an orexin deficiency state (Thannickal, Neuron 2000).
- In 10 narcolepsy patients versus 10 matched controls, olfactory detection, discrimination and identification were all significantly impaired; a subsequent double-blind placebo-controlled crossover in 7 of those patients showed improved odour detection thresholds with intranasal orexin A (Baier, Brain 2008).
- A double-blind, random-order, placebo-controlled crossover in 8 narcolepsy-with-cataplexy patients found significantly reduced total REM sleep (p=0.039) and reduced direct wake-to-REM transitions, but no statistically significant increase in wakefulness (Baier, Sleep Medicine 2011).
- The third and largest study examined sleep, wakefulness and attention in 14 patients and remains the biggest single human exposure to this peptide on record (Weinhold, Behavioural Brain Research 2014).
- The orexin-replacement strategy that reached phase 3 is a small molecule, not the peptide: oveporexton (TAK-861), an oral OX2R-selective agonist, met all primary and secondary endpoints (p<0.001) at week 12 in FirstLight (n=168) and RadiantLight (n=105).
limitations of the evidence
- Total human exposure across the entire published literature is 29 participants in three unregistered crossover studies from a single group, none powered for safety, and the same individuals may appear in more than one study.
- No study has quantified nose-to-brain delivery of orexin A in humans, so the central pharmacokinetics of the only route ever tested are unknown.
- The wake-promoting effect most often claimed for this peptide was specifically measured and not statistically significant in the overnight polysomnography study.
- All human work is in narcolepsy type 1, a deficiency state; nothing supports extrapolation to people with intact orexin neurons, in whom the receptors are already occupied by endogenous ligand.
- No published human pharmacokinetic or repeat-exposure safety data exist, so half-life, accumulation and immunogenicity are unknown.
- Orexin A is powerfully involved in autonomic and cardiovascular regulation, and no cardiovascular safety study of adequate size has ever been performed.
documented safety signals
- No serious adverse events have been reported in the three published intranasal studies, but with 29 participants in total this is an absence of study rather than evidence of safety.
- Orexin signalling raises sympathetic outflow and blood pressure in animal work, and intranasal orexin A in healthy men has been examined specifically for effects on sympathetic vascular tone; cardiovascular effects are therefore a plausible but essentially unstudied risk in humans.
- Orexin A is a potent appetite and arousal signal, so nonspecific systemic exposure would be expected to affect feeding and autonomic tone in ways no human study has characterised.
- Unlicensed material sold under this name has no pharmacopoeial identity, purity or endotoxin standard, and the disulfide-bonded structure means misfolded and reduced species are realistic contaminants.
identity
| full name | Orexin A (hypocretin-1), the 33-residue amidated neuropeptide processed from human prepro-orexin (HCRT) |
| category | Cognitive |
| modality | peptide |
| formula | C152H243N47O44S4 |
| molar mass | 3561.1 g/mol |
| cas | 205599-75-3 |
| sequence | pGlu-PLPDCCRQKTCSCRLYELLHGAGNHAAGILTL-NH2 (33 aa; N-terminal pyroglutamate, C-terminal leucinamide, disulfide bridges Cys6–Cys12 and Cys7–Cys14; residues 34–66 of human prepro-orexin, UniProt O43612) |
laboratory handling
| storage | Lyophilised powder is stored desiccated at -20 °C and protected from light. Once reconstituted, laboratory practice is refrigeration at 2-8 °C for short-term use, or aliquoting and freezing to avoid repeated freeze-thaw cycles. Handling information only; this material has no approved human use. |
| solubility | Short hydrophilic peptide, readily soluble in sterile or bacteriostatic water and in dilute aqueous buffer. Lot-specific solubility is stated on the certificate of analysis. |
| co-studied with | Not applicable. Co-administration with orexin receptor antagonists such as daridorexant would be directly pharmacologically opposed, and no human combination data of any kind exist for this peptide. |
Handling information describes laboratory practice for a research reagent. It is not a preparation guide for use in humans.
the receipts
7 citedClinicalTrials.gov, U.S. National Library of Medicine · 2026 · official
National Institute for Health and Care Excellence · 2023 · official
PubChem, National Library of Medicine · 2026 · reference
Neuron · 2000 · observational
Brain · 2008 · randomized
Sleep Medicine · 2011 · randomized
Takeda Pharmaceutical Company · 2025 · press release
Sources marked tertiary or press release are the weakest citations on this page.
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