Orexin A (hypocretin-1): what the narcolepsy studies found and what is unknown

Orexin A was discovered twice in 1998. Luis de Lecea and colleagues at the Scripps Research Institute found two peptides made only in the hypothalamus that excited neurons, and named them hypocretins for their hypothalamic origin and resemblance to the gut hormone secretin ^[1]. Weeks later Takeshi Sakurai, Masashi Yanagisawa and colleagues in Texas reported the same peptides as the ligands for two orphan receptors, showed they were made in the lateral hypothalamus, and named them orexins from the Greek for appetite because injecting them into rat brains made the animals eat ^[2]. Both names remain in use: orexin A and hypocretin-1 are the same molecule.

The two orexins come from a single precursor, prepro-orexin. Orexin A is 33 amino acids long with two internal disulphide bridges and binds both orexin receptors, OX1R and OX2R, while orexin B is 28 amino acids and prefers OX2R ^[2]. The neurons that make them, a few tens of thousands in humans, project widely to the arousal centres of the brainstem and to the cortex ^[3].

Within two years of its discovery, orexin was linked to narcolepsy. In 2000 Nishino, Mignot and colleagues reported that hypocretin-1 was undetectable in the cerebrospinal fluid of seven of nine people with narcolepsy ^[4], and Peyron and colleagues found a global loss of hypocretin-producing neurons in narcoleptic brains at post-mortem ^[5]. Narcolepsy type 1 is now understood as orexin deficiency, and a low CSF orexin A level is a diagnostic test for it. That is the scientific background against which research stores sell orexin A peptide as a wakefulness or focus aid, usually in vials and sometimes as an orexin nasal spray. PepFinder lists only vials.

Orexin neurons are active during waking and silent during sleep, and they drive the brain’s arousal systems, including the noradrenaline, histamine, serotonin, dopamine and acetylcholine cell groups, to hold the brain in a stable waking state. Sakurai’s 2007 review describes them as a switch that stabilises wakefulness and prevents the sudden transitions into REM sleep that characterise cataplexy ^[3]. The same neurons respond to energy status, which links wakefulness to feeding: fasting increases prepro-orexin expression ^[2], and central orexin stimulates food intake.

The peptide cannot easily reach the brain from the blood. That is why most human and animal studies use the intranasal route, on the theory that peptides can travel along the olfactory and trigeminal nerves directly into the brain. In anaesthetised rats, intranasal hypocretin-1 produced brain concentrations similar to intravenous dosing despite ten-fold lower blood levels, with about 80% of brain exposure attributed to direct nose-to-brain transport ^[6]. A 2018 PET imaging study in rodents and non-human primates was less encouraging: brain exposure to radiolabelled orexin A after intranasal dosing was poor, and uptake was similar to intravenous dosing across most brain regions, with possibly higher uptake only in the olfactory bulbs ^[7]. How much of an intranasal dose reaches the human brain is not known.

Where it does reach the brain, intranasal orexin A activates cortical and basal forebrain neurons. In rats, a single intranasal dose increased the marker c-Fos in the prefrontal cortex and in cholinergic neurons of the basal forebrain, and raised acetylcholine and glutamate release in the prefrontal cortex ^[8]. In aged rats, it altered attentional set-shifting as well as raising prefrontal acetylcholine ^[9].

Claims about orexin A benefits, from wakefulness to focus to fat loss, mostly borrow from the physiology of the natural peptide. The direct evidence for giving orexin A is summarised here.

Sleep deprivation in monkeys: in the best-known animal study, rhesus monkeys kept awake for 30 to 36 hours performed poorly on a memory task, and orexin A restored performance whether given intravenously (2.5 to 10 µg/kg) or by a nasal spray at an estimated 1 µg/kg. The nasal route was more effective than the highest intravenous dose, the benefit was specific to sleep-deprived animals and to the hardest trials, and brain glucose metabolism changes caused by sleep loss were reversed ^[10]. This 2007 study is the origin of interest in orexin A for shift workers and the military; it has not been replicated in humans.

Appetite: intranasal hypocretin-1 increased food consumption and activity in rats ^[11]. This is the opposite of what fat-loss marketing implies, and it is consistent with the peptide’s name.

Motion sickness: in a 2024 study, orexin A reduced nausea-like behaviour and hypothermia in rotated rats and, given intranasally to cats, reduced vomiting comparably to scopolamine ^[12]. No human study exists.

Sympathetic nervous system: in ten healthy young men, 500 nmol of intranasal orexin A raised resting muscle sympathetic nerve activity compared with placebo, without changing blood pressure or heart rate at rest ^[13]. This shows the peptide has a measurable central effect in healthy humans, and also that it activates the stress arm of the nervous system.

A group in Kiel, Germany, ran the human studies, all small, double-blind and placebo-controlled with a crossover design. In 2008 they showed that people with narcolepsy with cataplexy have a mildly impaired sense of smell, and that in seven patients a single intranasal dose of orexin A raised the odour detection threshold compared with placebo ^[14]. In 2011, eight patients received 435 nmol of recombinant hypocretin-1 intranasally before a night’s sleep: it did not significantly change wakefulness, but reduced REM sleep in the second half of the night, stabilised REM sleep and cut direct transitions from wake into REM ^[15].

In 2014 the same group gave 435 nmol of intranasal orexin A or placebo in the morning to 14 patients. After orexin A, patients had fewer wake-to-REM transitions and less REM sleep, more stage N2 sleep the following night, and fewer false reactions in a test of divided attention. The maintenance-of-wakefulness test did not show an increase in daytime alertness ^[16]. In other words, the peptide acted as a REM-sleep stabiliser and had a small effect on attention, but it did not simply make narcoleptic patients more awake.

Those three studies, involving fewer than 30 patients in total, are the entire published clinical record for orexin A in narcolepsy, and there has been no follow-up trial in more than a decade. The field moved instead to small-molecule orexin receptor agonists that can be taken by mouth. In September 2026 the New England Journal of Medicine published two phase 3 trials of oveporexton (TAK-861), an oral OX2R-selective agonist, in 273 people with narcolepsy type 1: it increased sleep latency on the maintenance-of-wakefulness test by 14 to 20 minutes versus almost no change with placebo, cut Epworth sleepiness scores by around 10 points, and reduced weekly cataplexy by 79 to 89%, at the cost of urinary frequency and transient insomnia in most participants ^[17]. Oveporexton is a different molecule from orexin A and its results do not transfer to the peptide.

In humans, effects were measured within 30 to 45 minutes of intranasal dosing in the sympathetic nerve study ^[13] and over the same night or day in the narcolepsy studies ^{[15] [16]}. In monkeys, the cognitive effect was tested immediately after dosing ^[10]. The peptide is cleared quickly from blood, and in the rat pharmacokinetic study brain and blood levels were followed over two hours ^[6]. No human study has measured duration of action beyond a single session, and nothing is known about repeated daily use.

These are doses used in studies under medical supervision. They are not recommendations, and the human studies were single doses in a laboratory. Intranasal, humans: 435 nmol of recombinant hypocretin-1 in the two Kiel sleep studies, which at a molecular weight of about 3,561 g/mol is roughly 1.5 mg ^{[15] [16]}; 500 nmol, roughly 1.8 mg, in the healthy volunteer sympathetic study ^[13]. Monkeys: 2.5 to 10 µg/kg intravenously and an estimated 1 µg/kg by nasal spray ^[10]. Rats: intranasal doses in the pharmacokinetic and neurochemistry studies ^{[6] [8]}.

These milligram-scale intranasal doses are far higher than the microgram amounts quoted on most vendor sites, which reflects how little of the peptide is thought to reach the brain. Vendor orexin A dosing charts are not derived from these studies. Our peptide calculator and the orexin A calculator page convert vial contents into concentrations for record-keeping; they do not imply a dose.

Every human study used the intranasal route ^{[13] [14] [15] [16]}, and the monkey study compared intravenous with nasal delivery ^[10]. We found no human study of subcutaneous orexin A, and given the peptide’s poor entry into the brain from blood, there is no reason to expect a subcutaneous injection to affect wakefulness. The oral route is not used because the peptide would be digested. An orexin A nasal spray is therefore the only form with any human data, and even then the PET study suggests most of the dose does not reach the brain ^[7].

Research stores sell orexin A as a freeze-dried powder, typically in 1 mg or 5 mg vials, for reconstitution with bacteriostatic water, and some sell pre-mixed sprays. PepFinder lists only vials. A 33-residue peptide with two disulphide bonds is difficult to make correctly, which matters for testing (see below).

The human studies reported no serious adverse events, but they involved fewer than 40 people, each dosed once or twice. The clearest measured effect in healthy humans is activation of the sympathetic nervous system ^[13], which in the long run is not obviously desirable. Orexin also increases food intake in animals ^{[2] [11]}, so an appetite-stimulating effect is plausible. Oveporexton, which activates the same receptor system, caused urinary frequency and insomnia in most trial participants ^[17]; whether the peptide does the same at effective brain concentrations is unknown because such concentrations have not been reliably achieved.

Two mechanistic concerns deserve mention. Orexin signalling is involved in reward and drug-seeking behaviour, and in stress and anxiety responses, in animal studies, so a wakefulness peptide is not a neutral stimulant. And repeated dosing with a natural peptide raises the possibility of an immune response; narcolepsy type 1 itself is thought to be autoimmune destruction of orexin neurons, and no study has examined whether giving exogenous orexin A affects that process. None of this has been studied because no one has given orexin A to people for more than a day or two.

Products sold as orexin A are unregulated. Our guides to spotting a fake peptide supplier and what research peptides are apply.

Orexin A is often searched alongside other wakefulness or sleep compounds. Modafinil is a licensed medicine for narcolepsy with large trials; orexin A has three small studies. Semax and Selank are Russian peptides sold for focus and anxiety with a different mechanism and their own small human literature. DSIP, delta sleep-inducing peptide, is marketed for the opposite purpose. Orexin A is unusual among research-store peptides in having a clear, well-established physiology and a disease defined by its absence; what it lacks is a way to get enough of it into the human brain.

Orexin A is not an approved medicine in any country. Oveporexton, an oral small molecule that activates the orexin 2 receptor, was approved for narcolepsy type 1 in 2026 after the phase 3 trials described above ^{[17] [18]}, but that approval covers a different compound, not the peptide. Orexin A is not on the US FDA’s list of compounding bulk substances that were nominated and withdrawn, nor in its category 2 list, so it has no compounding status; it is an unapproved research chemical. See our legal status overview, including the UK and US pages.

Orexin A is a large peptide with two disulphide bonds and a methionine residue, both of which can be damaged by oxidation, and it adsorbs to plastic. It should be kept freeze-dried, cold, dry and away from light, and solutions refrigerated and used quickly. See our peptide storage guide.

Correct folding of the two disulphide bridges is what distinguishes active orexin A from an inactive chain of the same amino acids, and a standard HPLC purity figure does not prove it. A certificate of analysis should show a measured mass close to 3,561 g/mol; see how to read a peptide COA and our guide to third-party peptide testing for what to ask for.

You can compare orexin A prices, including orexin A in the UK, in the US and in Europe, and see our list of third-party tested suppliers. A listing is not a statement that a product is legal to buy or appropriate to use.