Levels of opioid physical dependence in heroin addicts

The levels of opioid physical dependence in a group of long-term heroin addicts were ascertained by measuring the severity of the opioid withdrawal syndrome before and after pharmacological challenge with either 0.4 mg naloxone or placebo. Prior to challenge, patients manifested some subjective symptoms but few objective signs of opioid withdrawal. Patients who received placebo (n = 18) showed a significant increase in the mean score on one of three rating scales used to assess opioid withdrawal. Patients who received naloxone (n = 58) showed significant increases in mean scores on all three rating scales, but this was due primarily to increases observed in a minority of patients. Sixty-one percent of patients failed to manifest clinically significant changes in subjective symptoms, and 74% of patients failed to manifest clinically significant changes in objective signs of opioid withdrawal following naloxone administration. The results suggest that a substantial subgroup of heroin addicts are able to use opioids regularly while maintaining relatively low levels of physical dependence.