This is a 13 week outpatient clinical trial. Participants will either receive ondansetron or placebo and behavioral therapy. There is a 1, 2, and 3 month post-study follow up visit.Screening for this study is initially done over the telephone and takes 15-20 minutes. If participants are eligible after the initial screen, they will be invited to come in for a more thorough in house screen which takes about 5 to 6 hours. The screening will include a physical exam, review of medical, alcohol and drug histories and blood collection. If participants are found to be eligible after the in house screen, they will be enrolled in the 13 week outpatient clinical trial.