Ultimately, each person must choose for himself or herself. There is no way to get anyone to stop a bad habit against their will. And to do so would be an act of violence.
Even when people are sent to prison or rehab, they find ways to sneak alcohol in, or they return to alcohol (or drugs) as soon as they get a chance.
I am a strong believer in recovery. But recovery must come from without. The most we can do for another is encourage, and, at the right moment, confront.
Here are some excellent resources: Hubs by Billybuc; The first 70 pages of horror writer Stephen King's On Writing, which is an autobiography including his drug addiction, alcohol addiction, and his family's successful confrontation, and the move 28 Days with Sandra Bullock, a comedy about recovery, but a meaningful one.
If you are facing this in a family, there is a lot you can learn and a lot of support you can get. If you are thinking about a professional career helping addicts recover, then I wish you the best - your talents are desperately needed!