Pretty certain it is part of a series - there is a demon kept in a sideshow/freakshow and someone is tapping it for blood. Anybody?
The tapping for blood (of a kept person) reminds me of a somewhat minor point (in the grand scheme of things) of True Blood. Did you happen to read the Sookie Stackhouse Series? I don’t know whether or not that part was drawn from the books.
Long shot, I know, but I thought I’d toss it out there.
Bugger, I forgot to mention it wasn’t a vampire book.
I seem to remember that the demon’s blood was being tapped in New Jersey or Long Island. I think it was being used for some sort of evil project, but I might be conflagrating it with another book series.
I believe that the book you are looking for is All The Rage by F. Paul Wilson. It is part of the Repairman Jack series of books. A creature called a Rakosh is kept in a freak show and its blood is used to make a drug called Loki.
Seconded–I thought exactly the same thing when I read the OP.
Bingo =) Just looked online for the plot and that is definitely it. I think I need to ask for the whole series, it was an interesting read.