This is a 12-week, placebo-controlled trial of naltrexone (50 mg orally) in 163 problem drinkers. Problem drinkers are those individuals whose drinking puts them at risk of a variety of psychosocial and medical problems, including alcohol dependence, but who are not physically dependent on alcohol. They are estimated to comprise up to 20% of the general population. The study employed a factorial design in which the effects of medication (naltrexone vs. placebo), schedule of medication administration (i.e., daily vs. targeted), and the interaction of these factors on drinking behavior were examined. Targeted administration refers to the use of medication to cope with anticipated high-risk drinking situations.