Orexin B

What orexin B is

From the precursor prepro-orexin, the body cuts out two peptides: orexin A with 33 and orexin B with 28 amino acids. Both are also called hypocretin-1 and hypocretin-2, because two research groups described them independently of each other in 1998 – one via the receptors they activate, the other via the genes in the hypothalamus.

The cells that produce these peptides are located in the lateral and posterior hypothalamus. They keep the waking state stable, and when they die, narcolepsy type 1 develops, with daytime sleepiness and cataplexy. This is exactly what makes the system interesting for medicines.

In the trade, orexin B is found as a laboratory peptide with the label “for research purposes only”, often advertised as an agent against daytime fatigue or brain fog. In the scene it appears together with other neuropeptides, such as DSIP, which promises the opposite direction.

How it is supposed to work

Orexin A binds to both orexin receptors; orexin B prefers receptor 2 (OX2R). This preference is robust enough that a research tool was derived from it in 2003: an OX2R-selective agonist based on orexin B.

The catch lies not in the receptor but in the route to it. In 1999, Kastin and Akerstrom compared both peptides in mice: labeled orexin A passed from the blood into brain tissue by simple diffusion and arrived there mostly intact. Orexin B was broken down rapidly in the blood, could no longer be detected in intact form in the brain after intravenous administration and, with an octanol partition coefficient of 0.030 versus 0.232, is considerably less fat-soluble.

That is why the human experiments on the orexin system work either with intranasal orexin A or with small molecules that occupy the receptor directly and can be swallowed. For orexin B, this route does not exist.

What the studies show

The discovery in 1998

Sakurai and colleagues described two new neuropeptides from the same precursor that activate two previously orphan receptors, and found them in nerve cells in and around the lateral hypothalamus; administered into the brain, they increased food intake in rats, which is the origin of the name orexin. In parallel, the group around de Lecea described the same peptides as hypocretins with an excitatory effect on nerve cells.

The route into the brain (1999)

Kastin and Akerstrom tested in mice whether the peptides pass from the blood into the brain. Orexin A did so quickly, non-saturably and as an intact peptide right into brain tissue. Orexin B, by contrast, was so unstable in the blood that no intact peptide was found in the brain after peripheral administration. This paper is the reason why orexin B was never pursued further as an agent.

Intranasal orexin A in narcolepsy (2011 to 2018)

Weinhold and colleagues gave 14 people with narcolepsy with cataplexy intranasal orexin A in a blinded crossover experiment. Transitions directly from wakefulness into REM sleep decreased, REM duration fell, and in a divided attention test the patients made fewer errors; they did not become more awake. A 2018 PET study with labeled orexin A additionally put the nasal route into perspective: uptake into the brain was low and roughly corresponded to intravenous administration; only in the olfactory bulb was it possibly higher.

Oveporexton: the system works, the peptide is not it (2025 and 2026)

In the phase 2 trial, 90 people with narcolepsy type 1 received the oral OX2R agonist and 22 received placebo; sleep latency in the maintenance of wakefulness test rose by 12.5 to 25.4 minutes depending on the group. The two phase 3 trials confirmed this over 12 weeks and at the same time showed the price: side effects in 86 to 89 percent of those treated versus 43 to 54 percent under placebo, mainly more frequent urination and temporary insomnia.

Where the data stop

For orexin B as an agent there is no human study, no registry entry and therefore no information on what it does in healthy people. The findings implied in the advertising – wakefulness, concentration, mood – come either from basic research on the system or from other substances.

The animal and cell findings specific to orexin B concern heart muscle cells, adipose tissue, ovarian cells and nerve cells. None of them has been confirmed in humans, and several papers show that orexin A and orexin B behave differently in tissue – what was found for one does not automatically apply to the other.

Finally, it remains open what a peptide is supposed to achieve whose target receptor has been reachable since 2026 with a tested, swallowed active substance. For use in healthy people without narcolepsy, data are lacking there too.

Status, approval and legal

Orexin B is not an approved medicine in Germany or the EU. As a food supplement it would need an authorization under the Novel Food Regulation (EU) 2015/2283, which does not exist. It is sold as a laboratory chemical for research purposes.

A different substance is approved at the orexin system: on August 5, 2026, the US Food and Drug Administration (FDA) granted approval for oveporexton under the name Orzeyful, for adults with narcolepsy type 1. The agency also names the limitations: not tested in minors, not together with strong CYP3A inhibitors, and classification under US controlled substances law had been recommended but was still open at the time of approval. According to the sources available to us, the active substance is not yet approved in the EU.

In sport, group S0 of the World Anti-Doping Agency applies to the peptide: pharmacologically active substances without approval for therapeutic use in humans are prohibited at all times, even if they are not named on the list.

Safety

For the peptide there are no tolerability data in humans – no dose finding, no toxicology, no experience from use. What activation of the target receptor triggers can only be read from the approved active substance, and there the majority of those treated experienced increased urinary urgency, more frequent urination or temporary insomnia, plus increased salivation.

More important than any list of side effects here is how the symptom is handled: persistent daytime sleepiness, sleep attacks or sudden muscle weakness with emotions call for evaluation by a sleep medicine specialist. Narcolepsy type 1 is treatable, and self-experimentation with laboratory products delays the diagnosis. With research-grade products, content, purity and sterility are also untested.

Sources

• Sakurai et al., Cell 1998 – first description of orexin A and orexin B and their receptors
• de Lecea et al., PNAS 1998 – the hypocretins as hypothalamus-specific peptides
• Kastin and Akerstrom, J Pharmacol Exp Ther 1999 – orexin A, but not orexin B, passes from blood to brain
• Asahi et al., Bioorg Med Chem Lett 2003 – OX2R-selective agonist based on orexin B
• Van de Bittner et al., ACS Chem Neurosci 2018 – PET measurement of brain uptake of intranasal orexin A
• Weinhold et al., Behav Brain Res 2014 – intranasal orexin A in narcolepsy with cataplexy, 14 patients
• Dauvilliers et al., N Engl J Med 2025 – oveporexton in the phase 2 trial in narcolepsy type 1
• Dauvilliers et al., N Engl J Med 2026 – oveporexton in two phase 3 trials in narcolepsy type 1
• FDA, press release of August 5, 2026 – approval of Orzeyful (oveporexton)
• ClinicalTrials.gov – search for orexin B without a study on the peptide
• NADA – Prohibited List 2026, informational German translation (group S0)