This experiment will be conducted pretreatment and after 2 weeks on naltrexone. The primary aim of this pilot study is to examine weight gain in participants who complete the clinical trial treatment. Weight gain for those who are continuously abstinent for the last 4 weeks of treatment and rates of adverse events will be secondary outcomes. The effects of naltrexone on odor/food palatability, incentive value, and alliesthesia will be exploratory outcomes. Effect size estimates for weight gain will be generated for a NIH grant application.