“It is truly awful to admit that, glass in hand, we have warped our minds into such an obsession for destructive drinking that only an act of Providence can remove it from us.” (Twelve Steps and Twelve Traditions)
Per the 1913 Webster’s dictionary of US American English:
“Obsession: 1. The act of besieging. 2. The state of being besieged; used specifically of a person beset by a spirit from without.”
The so-called mental obsession is not therefore me constantly thinking about alcohol but the thought of a drink, the spirit (or spirits), hijacking me.