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I tried this once to my friend who used to drink a lot of alcohol and spend a lot of money in gambling. I advised him many times that he will lose his money and told him to prohibit from these activities but he did not listen me. In fact he become enemy of me and did not what to meet me anymore. The point of telling this that most people don't listen to others and keep thinking they are doing right.
And that's why there are professionals who know how to talk to such people, cos they are trained this way. Unless you are one of them, you shouldn't waste your time(and risk your friendship) trying to convince your friend to get out of his addiction. It's a common knowledge that the probability of you succeeding with that is very low.