 The overall aim of this project is to test the efficacy of naltrexone as a pharmacotherapy for excessive drinking when delivered to at-risk or problem drinkers who are seeking smoking cessation treatment. The proposed clinical trial uses a between-subjects design in which 300 at-risk or problem drinkers seeking treatment for smoking cessation will be randomly assigned to receive either daily 50 mg naltrexone or placebo. Medication will be initiated 2 weeks prior to participants smoking quit date and continue for 10 weeks. All participants also will receive transdermal nicotine patch and a counseling and medication management intervention that provides advice for smoking cessation, advice regarding the effects of heavy drinking on both smoking cessation and health, and monitoring and encouragement of compliance with medications. Drinking and smoking outcomes will be assessed at 2, 8, 16, and 26 weeks after participants smoking quit date. The primary aim of the study is to test the hypothesis that naltrexone will result in greater reductions in heavy drinking relative to placebo. The secondary aim will test whether naltrexone results in superior smoking outcomes relative to placebo, and tertiary aims will examine interrelationships among motivation for changing drinking, compliance with naltrexone, and drinking and smoking outcomes. 