biology

Orexin receptor

Orexin receptor is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Orexin receptor rather than just read about it. In short: The orexin receptor (also referred to as the hypocretin receptor) is a G-protein-coupled receptor that binds the neuropeptide orexin. There are two variants, OX1 and OX2, each encoded by a different gene (HCRTR1, HCRTR2).

Key takeaways

Orexin receptor belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Orexin receptor to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Orexin receptor from memory before moving on to harder problems.

Reference excerpt

The orexin receptor (also referred to as the hypocretin receptor) is a G-protein-coupled receptor that binds the neuropeptide orexin. There are two variants, OX1 and OX2, each encoded by a different gene (HCRTR1, HCRTR2). Both orexin receptors exhibit a similar pharmacology – the 2 orexin peptides, orexin-A and orexin-B, bind to both receptors and, in each case, agonist binding results in an increase in intracellular calcium levels. However, orexin-B shows a 5- to 10-fold selectivity for orexin receptor type 2, whilst orexin-A is equipotent at both receptors. Several orexin receptor antagonists are in development for potential use in sleep disorders. The first of these, suvorexant, has been on the market in the United States since 2015. There were two orexin agonists under development as of 2025: oveporexton and TAK-360.

Ligands Several drugs acting on the orexin system are under development, either orexin agonists for the treatment of conditions such as narcolepsy, or orexin antagonists for insomnia. In August 2015, Nagahara et al. published their work in synthesizing the first HCRT/OX2R agonist, compound 26, with good potency and selectivity. No neuropeptide agonists are yet available, although synthetic orexin-A polypeptide has been made available as a nasal spray and tested on monkeys. One non-peptide antagonist is currently available in the U.S., Merck's suvorexant (Belsomra), two additional agents are in development: SB-649,868 by GlaxoSmithKline, for sleep disorders, and ACT-462206, currently in human clinical trials. Another drug in development, almorexant (ACT-078573) by Actelion, was abandoned due to adverse effects. Lemborexant, an orexin receptor antagonist, was approved for use in the United States in 2019. Most ligands acting on the orexin system so far are polypeptides modified from the endogenous agonists orexin-A and orexin-B, however there are some subtype-selective non-peptide antagonists available for research purposes.

Agonists

Non-selective Orexins – dual OX1 and OX2 receptor agonists Orexin-A – approximately equipotent at the OX1 and OX2 receptors Orexin-B – approximately 5- to 10-fold selectivity for the OX2 receptor over the OX1 receptor AEX-5 – selective OX1 receptor agonist; also a cathepsin H inhibitor and dopamine reuptake inhibitor AEX-19 – dual OX1 and OX2 receptor agonist AEX-24 – selective OX2 receptor agonist; also an "S1R" agonist

Selective Alixorexton (ALKS-2680) – selective oral OX2 receptor agonist ALKS-7290 – selective OX2 receptor agonist ALKS-4510 – selective OX2 receptor agonist Balumorexton (TAK-360) – selective OX2 receptor agonist Cleminorexton (ORX750) – selective OX2 receptor agonist Danavorexton (TAK-925) – selective OX2 receptor agonist Firazorexton (TAK-994) – selective OX2 receptor agonist Ledasorexton (E-2086) – selective OX2 receptor agonist Oveporexton (Orzeyful; TAK-861) – selective OX2 receptor agonist SB-668875 – selective OX2 receptor agonist Suntinorexton – selective OX2 receptor agonist PhotOrexin – photoswitchable orexin-B analogue to control the OX2 receptor at nanomolar concentration in vivo.

Antagonists

Non-selective Almorexant (ACT-078573) – dual OX1 and OX2 receptor antagonist Daridorexant (Quviviq; ACT-541468) – dual OX1 and OX2 receptor antagonist Filorexant (MK-6096) – dual OX1 and OX2 receptor antagonist GSK-649868 (SB-649868) – dual OX1 and OX2 receptor antagonist Lemborexant (Dayvigo) – dual OX1 and OX2 receptor antagonist Suvorexant (Belsomra) – dual OX1 and OX2 receptor antagonist Vornorexant (ORN-0829, TS-142) – dual OX1 and OX2 receptor antagonist

Selective ACT-335827 – selective OX1 receptor antagonist AZD-4041 – selective OX1 receptor antagonist CVN-766 – selective OX1 receptor antagonist EMPA – selective OX2 receptor antagonist JNJ-10397049 – selective OX2 receptor antagonist Nivasorexant (ACT-539313) – selective OX1 receptor antagonist Rocavorexant (C4X-3256; INDV-2000) – selective OX1 receptor antagonist RTIOX-276 – selective OX1 receptor antagonist SB-334867 – selective OX1 receptor antagonist SB-408124 – selective OX1 receptor antagonist Seltorexant (MIN-202, JNJ-42847922, JNJ-922) – selective OX2 receptor antagonist TCS-OX2-29 – selective OX2 receptor antagonist Tebideutorexant (JNJ-61393215; JNJ-3215) – selective OX1 receptor antagonist

See also List of investigational insomnia drugs List of investigational narcolepsy and hypersomnia drugs

References

External links "Orexin Receptors". IUPHAR Database of Receptors and Ion Channels. International Union of Basic and Clinical Pharmacology. Orexin+Receptors at the U.S. National Library of Medicine Medical Subject Headings (MeSH)

Worked examples

Example 1 — a first encounter with Orexin receptor

Start with the simplest possible case. Write down what Orexin receptor claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Orexin receptor before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Orexin receptor ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Orexin receptor

In research: Orexin receptor appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Orexin receptor in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Orexin receptor is common in secondary-school and first-year university syllabi. It links to neighbouring topics G protein-coupled receptors, Genes on human chromosome 1, Genes on human chromosome 6, so understanding it makes those chapters shorter.
In everyday life: Look for Orexin receptor outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Orexin receptor” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Orexin receptor in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Orexin receptor means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Orexin receptor out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Orexin receptor in simple terms?

Why does Orexin receptor matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Orexin receptor?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Orexin receptor.