The study periods is 21 weeks during which the participant's have 8 appointments with the researchers. During the meetings research data will be collected and the participant is having Controlled Behavioral Therapy (CBT) consulting from a trained therapist. At the study visits, the subjects are given written instructions for the proper use of naltrexone and advised to take 50 mg naltrexone approximately one hour before gambling or feeling urges to gamble (and to refrain from taking naltrexone at other times). In this study the maximal daily dose is 50mg of naltrexone. The medication is free for the subjects.