**Core Concept**
Orexin receptor antagonists are a class of medications that target the orexin system in the brain. The orexin system plays a crucial role in regulating sleep-wake cycles. By blocking the action of orexins, these medications can help improve sleep quality and duration.

**Why the Correct Answer is Right**
Suvorexant is a dual orexin receptor antagonist that selectively blocks the orexin 1 (OX1) and orexin 2 (OX2) receptors. This action leads to a decrease in wakefulness and an increase in sleep duration. Suvorexant is specifically approved for the treatment of insomnia characterized by difficulties with sleep initiation and maintenance.

**Why Each Wrong Option is Incorrect**
**Option A:** Ramelteon is a melatonin receptor agonist, not an orexin receptor antagonist. It works by mimicking the action of melatonin to regulate the sleep-wake cycle.
**Option B:** Zolpidem is a GABA receptor agonist, which enhances the activity of GABA to induce sleep. It is not an orexin receptor antagonist.
**Option C:** Eszopiclone is a non-benzodiazepine hypnotic, which acts as an agonist at the GABA receptor. It is not an orexin receptor antagonist.

**Clinical Pearl / High-Yield Fact**
Orexin receptor antagonists like suvorexant are unique in their mechanism of action, which targets the orexin system rather than GABA or melatonin receptors. This makes them a valuable option for patients with insomnia who have not responded to other treatments.

**Correct Answer:** C. Suvorexant is approved for the treatment of insomnia.