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To stop addiction of any thing in any person the most important thing is the WILL power of a person .So if your fiancée wants to stop pan masala he has to stop it himself nobody can help.After he stops eating to control the effects or withdrawal symptoms
the doctor can give him the required medicines according to the symptoms.So tell him to consult a doctor & try to stop it & get medicines for withdrawal.
If he directly cannot stop get him to admit him in a hospital or a rehabilitation
center.There he will get help .