Orexin-A
hypocretin-1, Hcrt-1, OX-A
1What it is
Orexin-A is one of two peptides (with orexin-B) discovered in 1998 by two groups at once — hence the double name: Sakurai and colleagues called them orexins for their effect on appetite, de Lecea and colleagues called them hypocretins for their hypothalamic origin. They are made by only a few tens of thousands of neurons in the lateral hypothalamus, which project widely to every arousal system in the brain. Within two years it was shown that narcolepsy type 1 — the form with cataplexy — is caused by the loss of these neurons, with undetectable orexin-A in cerebrospinal fluid (Nishino 2000; Peyron 2000; Thannickal 2000). That made orexin-A the obvious replacement therapy, and the obvious problem: a 33-residue peptide that does not cross from blood into brain.
Orexin-A as a research peptide is therefore the natural hormone itself, synthesised. The pharmaceutical field has largely moved on to small molecules that mimic it (orexin-2 receptor , several in Phase 3 for narcolepsy as of 2026) or block it (suvorexant, lemborexant, daridorexant — approved for insomnia). The peptide remains an experimental tool with a handful of tiny human studies.
2How it's thought to work
3What the research shows
Sleep and wakefulness in narcolepsy
Olfactory function in narcolepsy
Cognition under sleep deprivation
Narcolepsy models
Appetite, reward, metabolism
Human healthy-volunteer or community use
4Reported side effects and interactions
Literature-reported
Single intranasal doses in the small narcolepsy studies were well tolerated with no notable adverse events. No repeated-dose human safety data.Community-reported
nasal irritation, raised heart rate or blood pressure sensation, jitteriness or anxiety, reduced appetite in some and increased in others, trouble sleeping if taken late. Very limited pool of reports.Theoretical. orexin signalling raises sympathetic tone and blood pressure in animals, a plausible concern in anyone with cardiovascular disease; it drives reward and motivated behaviour, which has been linked in rodents to drug-seeking, so there is a theoretical addiction-relevance question; long-term receptor adaptation with repeated dosing is unknown.
Interactions. none studied. Pharmacological opposites are the approved orexin antagonists (suvorexant, lemborexant, daridorexant); stimulants and caffeine would be expected to add to the arousal effect.
Markers researchers commonly monitor
No compound-specific lab markers exist for exogenous orexin-A. Physiology suggests:
| Marker | Why it's watched |
|---|---|
| Blood pressure and resting heart rate | orexin raises sympathetic outflow in animals; the single most relevant home measurement. |
| Sleep architecture or at least a sleep diary / wearable | the target effect is on sleep–wake timing and REM; a diary is cheap, a home sleep study is better. |
| Daytime sleepiness scale (e.g. Epworth) | the outcome narcolepsy trials care about. |
| Weight and appetite log | orexin affects both feeding and energy expenditure in rodents. |
| Fasting glucose | orexin interacts with glucose sensing and sympathetic control of metabolism in animals; a baseline is reasonable. |
| CBC and CMP | general baseline for a compound with no repeated-dose human safety data. |
Free for everyone. Safety information is never behind a paywall.
5Reconstitution and handling
Supplied as powder, often in sub-milligram to 1 mg vials because of cost. The two disulfide bonds make it more fragile than most linear peptides: gently with sterile or , do not shake, keep cold and protected from light, and avoid repeated freeze–thaw. For nasal use, dispense from a metered spray and calculate the dose per spray from the concentration. Human studies used a buffered nasal solution.
Open in calculator, pre-loaded →6Commonly studied alongside
Not usually combined. Conceptually paired with DSIP (the "sleep" peptide to orexin's "wake"), and discussed alongside modafinil, sodium oxybate and pitolisant as narcolepsy treatments in the literature. Ghrelin and leptin appear as upstream regulators in rodent studies.
Informational cross-links. Not stack recommendations.
7Regulatory status by region
| Region | Status (checked —) |
|---|---|
| United States | Not FDA-approved. Investigational only; the peptide is not a compounding substance. Orexin receptor antagonists are approved for insomnia; small-molecule OX2R agonists are in Phase 3 † |
| European Union | Not authorised |
| United Kingdom | Not licensed |
| Australia | Not approved |
| South Africa | Not registered |
| Sport (WADA) | Not specifically listed as of review date; as a non-approved substance it falls under S0 † |
8Open questions
- Does intranasal orexin-A reach the brain in humans in meaningful amounts, and how reproducibly?
- Repeated-dose safety and receptor adaptation — never studied.
- Any effect in people with intact orexin systems (healthy adults, shift workers) — no data.
- Whether the small-molecule make the peptide obsolete for narcolepsy, or whether the peptide's broader receptor profile offers anything distinct.
9References
- 1Sakurai T et al. (1998). Orexins and orexin receptors: a family of hypothalamic neuropeptides and G protein-coupled receptors that regulate feeding behavior. Cell. PubMed · DOI
- 2de Lecea L et al. (1998). The hypocretins: hypothalamus-specific peptides with neuroexcitatory activity. Proc Natl Acad Sci USA. DOI
- 3Nishino S et al. (2000). Hypocretin (orexin) deficiency in human narcolepsy. Lancet. PubMed · DOI
- 4Peyron C et al. (2000). A mutation in a case of early onset narcolepsy and a generalized absence of hypocretin peptides in human narcoleptic brains. Nat Med. PubMed · DOI
- 5Deadwyler SA et al. (2007). Systemic and nasal delivery of orexin-A (hypocretin-1) reduces the effects of sleep deprivation on cognitive performance in nonhuman primates. J Neurosci. PubMed · DOI
- 6Baier PC et al. (2008). Olfactory dysfunction in patients with narcolepsy with and without REM sleep behaviour disorder. Brain. PubMed
- 7Baier PC et al. (2011). Effects of intranasal hypocretin-1 (orexin A) on sleep in narcolepsy with cataplexy. Sleep Med. PubMed · DOI
- 8Weinhold SL et al. (2014). The effect of intranasal orexin-A (hypocretin-1) on sleep, wakefulness and attention in narcolepsy with cataplexy. Behav Brain Res. PubMed · DOI
References are being resolved to PubMed/DOI identifiers; links search PubMed for the citation until then.
† Being confirmed by our reviewers against current sources.
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Self-reported side effects Phase 2
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