Orpheus is a vampire drug, a mystical opiate which is taken in with the blood of those they feed from – the humans typically inject the drug into their bloodstreams before the feeding.
The enchanted drug can be easily tasted on the blood, and its effects on the vampire are very quick, especially if the dose is large. Of course, a dose that large will tend to knock out the human, leaving them in a comatose – and potentially fatal – state.
Smaller doses can be euphoric for both parties, but larger ones induce what can only be described as a vision quest, in which both parties travel through the history of the vampire in question, and choices made along the way determine whether either of them ever wakes up again. This experience of taking the drug has been described as being taken to Hell and left there.