Aims: To determine the impact of naloxone training on knowledge of opiate overdose and confidence and willingness to take appropriate action and to examine the use of naloxone and other harm-reduction actions at the time of overdose events. Methods: The evaluation was based on a repeated-measure design, whereby clients were tested before and after training. In total, 521 opiate users and four non-opiate users, drawn from five community sites (362) and three prison locations (163), completed pre- and post-test self-completed questionnaires. Actions taken at the time of overdose events by the naloxone group and a comparison group were compared using forms completed by agency staff. Findings: Knowledge about how to recognise and respond to overdose events increased among trainees across all measures. So too did perceived confidence in responding to them and willingness to carry out the recommended procedures. Over the course of the evaluation, there were 28 recorded uses of naloxone, resulting in 27 recoveries and one fatality. Conclusions: The study has shown that training in overdose management and the use of naloxone can bring about significant improvements in knowledge and willingness to take action. THN trainees also demonstrated that they were able to use naloxone successfully in overdose events. (Contains 6 tables and 1 note.)