In a randomized double-blind study, the clinical efficacy of methadone vs. methadone and guanfacine was assessed in terms of evolution of opioid withdrawal symptoms during inpatient detoxification. A total of 144 patients were included and randomly allocated to three different treatment groups: methadone alone, and two combined treatment schedules (methadone plus 3 or 4 mg of guanfacine). No differences were observed among the three groups with regard to retention rate throughout the study period. Both therapies, methadone and methadone plus guanfacine, determined a slight increase in withdrawal scores when methadone was discontinued. However, guanfacine was unable to effectively control methadone-associated withdrawal symptoms. These results indicate that guanfacine does not effectively reduce the opioid withdrawal symptoms.