The Beast is as real as addictive desire itself, for the simple reason that the Beast is addictive desire. That perverted survival drive did not always exist, but it certainly does now. It is worth noting, though, that the Beast is not the cause of your addiction, because the Beast cannot do anything on its own. It can only use the Addictive Voice to convince you to do what it wants you to do, which is obviously to drink/use.