Orexin-A
The peptide whose absence causes narcolepsy, and whose receptor is drugged in both directions
Orexin-A, also called hypocretin-1, is made by a small cluster of neurons in the hypothalamus and keeps the brain awake. Losing those neurons causes narcolepsy type 1. Blocking its receptor treats insomnia; activating the same receptor is now being tested to treat narcolepsy.
What is it?
Orexin-A and orexin-B were described in 1998, cut from one precursor and acting on two related receptors, with the neurons that make them confined to the lateral hypothalamus. Giving them centrally to animals changed feeding, which is where the name came from; the wakefulness role came later and turned out to be the important one.
Narcolepsy type 1 is the loss of those neurons, and orexin-A in cerebrospinal fluid is how it is diagnosed. Levels have been mapped across ages from infants to the elderly, found to fluctuate with season and daylight, and the intermediate range has been studied in its own right.
The drugs went in opposite directions from the same receptor. Blockers of both receptors are approved for insomnia. Activators selective for receptor 2 were developed for narcolepsy, and in 2026 the first, oveporexton, was approved for narcolepsy type 1 after two phase 3 trials.
More agonists are following. In a 92-person phase 2 trial, once-daily alixorexton kept people with narcolepsy type 1 awake about 22 to 26 minutes longer than placebo on a wakefulness test, at the cost of frequent urination, insomnia and excess saliva. A smaller study found it also worked in idiopathic hypersomnia and narcolepsy type 2, where orexin is not clearly missing.
Measurement still anchors the diagnosis. A 2026 comparison found one orexin-A assay reads about 1.5 times higher than the commercial kit, so a cut-off set on one does not transfer to the other. Low CSF orexin-A also turns up outside narcolepsy, as in juvenile Batten disease. On the blocker side, dual antagonists kept improving sleep over a year of trials, and pooled studies found no rise in falls or fractures.
Mechanism of Action
Orexin-A is a neuropeptide made by neurons in the lateral hypothalamus; it acts on the orexin 1 and orexin 2 receptors to keep the brain awake.
Wakefulness
Orexin signalling stabilises wakefulness; losing the neurons that make it causes narcolepsy type 1.
Agonists replace the signal
Oral orexin receptor 2 agonists such as oveporexton and alixorexton restore wakefulness in narcolepsy type 1.
Antagonists block it
Dual orexin receptor antagonists treat insomnia by dampening the same arousal signal.
Published Research
These are the studies in people, read from their PubMed abstracts: two agonist trials in narcolepsy, one blocker review and two measurement studies.
An oral agonist in narcolepsy type 1
In a phase 2 randomised placebo-controlled trial, 73 patients with narcolepsy type 1 received the oral orexin receptor 2 agonist TAK-994 twice daily at 30, 90 or 180 mg, or placebo, with sleep latency on the Maintenance of Wakefulness Test as the primary endpoint over eight weeks.
The successor molecule
In a phase 2 randomised placebo-controlled trial, 90 participants with narcolepsy type 1 received oveporexton, an oral orexin receptor 2 agonist, at several once- and twice-daily doses or placebo, measured on sleep latency, the Epworth Sleepiness Scale and weekly cataplexy rate.
Normal levels, infancy to old age
Orexin-A was measured in lumbar cerebrospinal fluid across age groups from infants to the elderly, establishing the range against which a narcolepsy diagnosis is read.
It moves with the seasons
Cerebrospinal fluid orexin-A fluctuated with season and correlated with daylight hours, which matters for interpreting a single measurement in a patient.
Vibrance-1: alixorexton
In 92 adults with narcolepsy type 1, once-daily alixorexton at 4, 6 or 8 mg extended time awake on the Maintenance of Wakefulness Test by 22 to 26 minutes over placebo at 6 weeks; frequent urination (55%), insomnia (28%) and excess saliva (25%) were the commonest side effects.
Alixorexton beyond NT1
In a phase 1b study, alixorexton produced dose-dependent gains in wakefulness in idiopathic hypersomnia and narcolepsy type 2, where orexin is not clearly lost, and a response at lower doses in narcolepsy type 1; there were no serious adverse events.
Measuring orexin-A in CSF
Comparing an in-house radioimmunoassay with the commercial kit, the in-house method read about 1.5 times higher and needed a narcolepsy type 1 cut-off of 153 pg/mL; intermediate levels (153 to 400 pg/mL) were found in 9.7% and linked to HLA-DQB1*06:02.
Orexin loss in CLN3 disease
In children and adolescents with juvenile Batten disease (CLN3), CSF orexin-A was reduced and fell further with disease duration, alongside narcolepsy-like symptoms, supporting it as a monitoring marker.
Borderline levels without cataplexy
A post-mortem case of narcolepsy without cataplexy and borderline low CSF hypocretin-1 showed almost complete loss of CRH neurons in the hypothalamic paraventricular nucleus, as seen in narcolepsy type 1.
Lower in new type 2 diabetes
Newly diagnosed, untreated type 2 diabetes patients had lower serum orexin-A and poorer heart rate variability than healthy controls, but the two measures did not correlate.
Salivary orexin and exercise
In young women, salivary orexin rose more after high-intensity interval training than after lower-intensity exercise, with a different time course from alpha-amylase and cortisol.
Suvorexant after heart surgery
In 100 ICU patients after cardiac surgery randomised to suvorexant or placebo, EEG-measured wake time, total sleep and delirium did not differ.
Blocking the same receptors for insomnia
A review of daridorexant, a dual orexin receptor antagonist developed for insomnia disorder: the same system drugged in the opposite direction from the narcolepsy agonists.
The first approved agonist
A 2026 review describes oveporexton, an oral orexin receptor 2 agonist, as the first approved therapy targeting the orexin pathway in narcolepsy type 1, with approval supported by two global phase 3 trials showing better wakefulness and fewer cataplexy attacks than placebo.
Blockers over a year
Across 6 randomised trials of 3,546 people with chronic insomnia, dual orexin receptor antagonists kept improving subjective sleep at 6 and 12 months; adverse events matched placebo at 6 months but were higher at 12.
Blockers and falls
In 19 studies with 183,595 participants, dual orexin receptor antagonists did not increase falls (odds ratio 0.76) or fractures (1.05), though the authors call the evidence in older adults limited.
Blocker dose response
A dose-response meta-analysis found that the sleep benefits of dual orexin receptor antagonists plateau within approved doses and does not support higher dosing.
Sepsis-associated encephalopathy
In mice with sepsis, orexin-A pretreatment improved survival and cognition, reduced blood-brain barrier leakage and inflammation, and protected endothelial junctions in cell experiments.
Dosing Data
Orexin-A itself is not given as a medicine. The rows below are oral receptor 2 agonists from narcolepsy trials.
Educational information, not medical advice. Each dose above is tagged with its source: an approved label, a published human study, animal data, or amounts reported by users. None is a recommendation for you. An unapproved compound has no established safe or effective human dose, and products sold for “research use only” are not made or tested for people. Talk to a doctor before acting on anything on this site, including before you start, stop or change any medicine or dose. Full medical disclaimer.
Side Effects & Contraindications
Reported Side Effects
Orexin-A itself is not given to people; these come from the drugs that act on its receptors.
Contraindications & Cautions
Not a medicine.
Legal Status
The peptide is not a drug; its receptors are drugged both ways.
Frequently Asked Questions
?What does orexin-A do?
It is made by a small cluster of hypothalamic neurons and keeps the brain awake, stabilising the boundary between sleep and wakefulness.
?What is its link to narcolepsy?
Narcolepsy type 1 is caused by the loss of those neurons, and measuring orexin-A in cerebrospinal fluid is how the diagnosis is made.
?Can it be taken as a drug?
No. The peptide itself is not given; the drugs that act on its receptor 2 are oral small molecules, one of which, oveporexton, was approved for narcolepsy type 1 in 2026.
?Why do some drugs block it?
Because blocking wakefulness is how you treat insomnia. The same receptor pair is targeted in both directions for opposite conditions.
?Is there an approved orexin drug for narcolepsy?
Yes. A 2026 review describes oveporexton, an oral orexin receptor 2 agonist, as the first approved therapy targeting the orexin pathway in narcolepsy type 1, supported by two phase 3 trials. It is a small molecule, not orexin-A.
?Are orexin blockers safe long term?
Pooled trials of up to a year found continued sleep benefit, with adverse events similar to placebo at 6 months and somewhat higher at 12, and no increase in falls or fractures across 19 studies.
References
- [pubmed] Dauvilliers Y, et al. "Oral Orexin Receptor 2 Agonist in Narcolepsy Type 1." N Engl J Med, 2023;389(4):309-321. PMID: 37494485.
- [pubmed] Dauvilliers Y, et al. "Oveporexton, an Oral Orexin Receptor 2-Selective Agonist, in Narcolepsy Type 1." N Engl J Med, 2025;392(19):1905-1916. PMID: 40367374.
- [pubmed] Kanbayashi T, et al. "Hypocretin-1 (orexin-A) levels in human lumbar CSF in different age groups: infants to elderly persons." Sleep, 2002;25(3):337-9. PMID: 12003164.
- [pubmed] Boddum K, et al. "Cerebrospinal Fluid Hypocretin-1 (Orexin-A) Level Fluctuates with Season and Correlates with Day Length." PLoS One, 2016;11(3):e0151288. PMID: 27008404.
- [pubmed] Dauvilliers Y, et al. "Daridorexant, a New Dual Orexin Receptor Antagonist to Treat Insomnia Disorder." Ann Neurol, 2020;87(3):347-356. PMID: 31953863.
- [pubmed] de Lecea L, et al. "The hypocretins: hypothalamus-specific peptides with neuroexcitatory activity." Proc Natl Acad Sci U S A, 1998;95(1):322-7. PMID: 9419374.
- [pubmed] Mahoney CE, et al. "The neurobiological basis of narcolepsy." Nat Rev Neurosci, 2019;20(2):83-93. PMID: 30546103.
- [pubmed] Sakurai T, et al. "Orexins and orexin receptors: a family of hypothalamic neuropeptides and G protein-coupled receptors that regulate feeding behavior." Cell, 1998;92(4):573-85. PMID: 9491897.
- [pubmed] Sun Y, et al. "Oveporexton: The first-in-class orexin receptor 2 (OX2R) agonist approved for treatment of narcolepsy type 1 (NT1)." Drug Discov Ther, 2026;20(4):357-359. PMID: 42618292.
- [pubmed] Plazzi G, et al. "Safety, tolerability, and efficacy of alixorexton, a selective orexin 2 receptor agonist for narcolepsy type 1 (Vibrance-1): a randomised, double-blind, placebo-controlled, phase 2 trial." Lancet Neurol, 2026;25(10):889-899. PMID: 42636845.
- [pubmed] Grunstein RR, et al. "Targeting Orexin 2 Receptors in Idiopathic Hypersomnia and Narcolepsy: A Randomised Phase 1b Proof-Of-Concept Study of Alixorexton." J Sleep Res, 2026:e70429. PMID: 42551881.
- [pubmed] Åkeby S, et al. "Analytical evaluation and method comparison of an orexin-A radioimmunoassay in cerebrospinal fluid: establishing a cut-off value for type 1 narcolepsy and exploring genetic and clinical characteristics." Sleep Med, 2026;148:109269. PMID: 42753384.
- [pubmed] Wasling P, et al. "Progressive Orexin Deficiency and Age-Dependent Glial and Axonal Biomarkers in juvenile neuronal ceroid lipofuscinosis type 3 (CLN3) Disease." Pediatr Neurol, 2026;181:114-120. PMID: 42314400.
- [pubmed] Shan L, et al. "Postmortem Evidence of CRH Neuron Reduction in Narcolepsy Without Cataplexy With Borderline Hypocretin-1 Levels." J Sleep Res, 2026;35(5):e70395. PMID: 42348342.
- [pubmed] Gebrye AT, et al. "Serum Orexin A Levels and Heart Rate Variability Parameters in Newly Diagnosed, Treatment-Naïve Type 2 Diabetes Mellitus: A Case-Control Study." Cureus, 2026;18(7):e112979. PMID: 42621168.
- [pubmed] Moscatelli F, et al. "An Integrated Multi-Biomarker Perspective on Acute Exercise: Differential Orexin, Alpha-Amylase, and Cortisol Responses Across Modalities." Sports (Basel), 2026;14(8). PMID: 42646889.
- [pubmed] Araujo LMM, et al. "Long-term use of dual orexin receptor antagonists for the treatment of insomnia: a systematic review and meta-analysis." Arq Neuropsiquiatr, 2026;84(7):1-10. PMID: 42595319.
- [pubmed] Paolone A, et al. "Use of Dual Orexin Receptor Antagonists for Insomnia and the Risk of Falls and Fractures: A Systematic Review and Meta-Analysis." J Am Geriatr Soc, 2026. PMID: 42799573.
- [pubmed] Caiazza C, et al. "Dose-response meta-analysis of dual orexin receptor antagonists on sleep parameters and implications for orexin-mediated arousal." Sleep Med, 2026;148:109249. PMID: 42710466.
- [pubmed] Wongtangman K, et al. "Effect of the orexin receptor antagonist, suvorexant, on sleep architecture in the early postoperative period following cardiac surgery: a randomized controlled trial." Crit Care, 2026;30(1). PMID: 42337809.
- [pubmed] Xiong D, et al. "Perioperative orexin-A protects brain microvascular endothelial integrity in experimental sepsis-associated encephalopathy." Neuropeptides, 2026;120:102652. PMID: 42715798.
Sources & Citations
Studies were read from their PubMed abstracts; orexin-A has no label. Read October 7, 2026.
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