Societies recent obsession with the undead, zombies is the flavor of the moment + psychoactive drug that inhibits rational thinking and reasoning, amplifies emotional impulse, while wrecking general havoc and destruction of the mind of the user = drug crazed cannibals.

No demons required.

Saves Satan some foot soldiers for more trying matters. Free will allows said person to willingly take said substance of the month.

That's all too human. You can't blame the devil for the poor choices of an individual.

Satan is a tempter first and foremost. Drugs are one of very many things he offers and makes appealing to take. Satan will get his for his part. Rest assured. Satan's doom was foretold before our Lord Jesus Christ's first coming, and so he works to the end of wickedness because Satan knows his time is short.

But it needs to be said that genuine demonic possession is an exceedingly rare phenomenon. Unmistakable and mostly unprovable.

Drug induced violence, even drug induced cannibals aren't anything special when you look behind the curtain. Just another symptom of the sin condition, the result of a poor choice on the end of the individual come to fruition.

Satan sells sin and we're buyers.

The one that sows sin reaps death, regardless of his merchant: Be it Satan or otherwise. To that end, we don't need Satan's help to be wicked.

All of us are home brewers of sin and wickedness of every kind.