Objective:μ-Opioid receptor blockade during general anesthesia is a new treatment for detoxification of opioid addicted patients. We assessed catecholamine plasma concentrations, oxygen consumption, cardiovascular variables, and withdrawal symptoms after naloxone and tested the hypothesis that variables are influenced by the anesthetic administered during detoxification.Design:Prospective randomized clinical study.Setting:Intensive care unit of a university hospital and psychiatric ward.Patients:Twenty-five mono-opioid addicted patients with mild to moderate systemic disease (ASA II classification) in a methadone substitution program.Intervention:General anesthesia with either propofol (129 ± 7 μg·kg−1·min−1, mean ± SEM) or methohexital (74 ± 14 μg·kg−1·min−1), μ-opioid receptor blockade by naloxone in a stepwise fashion (increasing doses of 0.4 mg, 0.8 mg, 1.6 mg, 3.2 mg, and 6.4 mg at 15 min intervals followed by 0.8 mg·hr−1for 24 hrs) and naltrexone 50 mg·day−1orally for ≥4 wks. Clonidine was started 180 mins after the first naloxone dose and its infusion rate was individually adjusted to mitigate withdrawal symptoms during weaning and after extubation.Measurements and Main Results:During propofol and methohexital anesthesia, naloxone induced a 30-fold increase in epinephrine and a significant three-fold increase in norepinephrine plasma concentrations without a significant difference between groups. This increase in catecholamine plasma concentrations was associated with increased oxygen consumption and marked cardiovascular stimulation with both anesthetics, as shown by increased cardiac index, heart rate, and systolic atrial pressure whereas diastolic pressure remained unchanged. Patients receiving propofol could be extubated significantly earlier after discontinuation of the anesthetics. Although the maximum degree of withdrawal symptoms (Short Opioid Withdrawal Scale) on the day after detoxification was similar with both anesthetics, subsequent withdrawal symptoms decreased significantly more rapidly after propofol anesthesia.Conclusions:Naloxone treatment, in opioid-addicted patients, induced a marked increase in catecholamine plasma concentrations, metabolism, and cardiovascular stimulation during anesthesia with both propofol and methohexital. Although both anesthetics appear suitable for detoxification treatment, the use of propofol is associated with earlier extubation and, surprisingly, a shortened period of long-term withdrawal symptoms during detoxification.