"Cunning, baffling, powerful". It's a liquid toxin which floods the brain with chemicals that impact upon the brains healthy pleasure/reward system, such that it becomes habitual and an addiction arises,: accompanied by resultant cravings, urges, compulsions (old-style obsessions) are borne, as a new, rogue survival drive.
I'm sorry for your friend's plight, he desperately needs a professional detox, followed by a place to stay. Has your friend attended AA?
Edited to add - I'm relieved he's safe and in a centre.