© 2017, Springer International Publishing AG. Background: Alcohol dependence remains a major health problem from both a public health and clinical perspective. Harm reduction strategies have been increasingly recognized as suitable treatment goals. Nalmefene has been recently approved for this precise therapeutic indication after completion of phase III trials. However, more data from routine practice settings are needed in order to obtain evidence with high external validity. The aim of this study was to conduct a single-arm, phase IV study with alcohol-dependent outpatients starting nalmefene for the first time. Methods: An observational, multisite, single-arm, phase IV study was conducted among adult alcohol-dependent outpatients who received nalmefene for the first time. The study consisted of four visits: baseline, 4 weeks (referred to as 1 month hereafter), 6 and 12 months. At each visit, drinking variables were obtained from the Timeline Followback regarding the previous month. Satisfaction with medication was also assessed for both patients and professionals, with the Medication Satisfaction Questionnaire. A repeated measures mixed model was performed for effectiveness analysis regarding drinking outcomes (reduction in total alcohol consumption and number of heavy drinking days). Regression analyses were performed in order to find predictors of response to nalmefene. Results: A total of 110 patients were included, with 88 reporting data at the 1-month visit. On average, patients took nalmefene 68% of the days. The number of heavy drinking days decreased from 13.5 to 6.8 days/month, and total alcohol consumption decreased from 169 to 79 units. For both outcomes, significant reductions at 1 month were found, with no other significant variables reaching significance. Thirty-seven patients were considered medication responders, but given the high presence of low-risk drinkers in our sample, no significant predictors could be found. Satisfaction was globally high for both professionals and patients, and overall nalmefene was well tolerated, with no serious adverse events reported. Conclusion: The data provided by this phase IV study suggest nalmefene is an effective, well-tolerated treatment for alcohol dependence in real-world, clinical settings.